Review of the Formaldehyde Assessment in the National Toxicology Program 12th Report on Carcinogens (2014)

Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

2 Review of the Formaldehyde Profile in the National Toxicology Program 12th Report on Carcinogens To address the first part of its statement of task, this committee reviewed the formaldehyde substance profile in the National Toxicology Program (NTP)’s 12th Report on Carcinogens (RoC) (NTP 2011). The committee’s review was informed by many documents, including those in Table 1-1. The committee also examined the primary literature cited in the background document for formalde- hyde and other literature published by June 10, 2011 (the date when the 12th RoC was released). The headings and structure of the present chapter parallel the major headings that NTP used in the substance profile for formaldehyde— that is, cancer studies in humans, cancer studies in experimental animals, other relevant data, and studies of mechanisms of carcinogenesis. The committee also reviewed the following sections in the substance profile: properties, use, produc- tion, exposure, regulations, and guidelines. As part of its review, the committee determined whether NTP had de- scribed and conducted its literature search appropriately, whether the relevant literature identified during the literature search was cited and sufficiently de- scribed in the background document, whether NTP had selected the most in- formative studies in making its listing determination, and whether NTP’s argu- ments supported its conclusion that formaldehyde is known to be a human carcinogen. Instead of discussing the strengths and weaknesses of each study in detail as part of this chapter, the committee chose to discuss such detail as part of its independent analysis in Chapter 3. Detailed data from individual studies can be found in Chapter 3 and in the background document for formaldehyde (NTP 2010). On the basis of its review and analysis of the substance profile, the committee ends this chapter with a review of NTP’s literature-search methods, suggestions of clarifications that NTP could make to improve future iterations of the background document or substance profile for formaldehyde, and an assess- ment of whether the evidence presented by NTP in the background document and the substance profile support the listing of formaldehyde as a known human carcinogen in the 12th RoC. 33 

34 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens CARCINOGENICITY NTP began the substance profile with a clear statement of its conclu- sions—that is, formaldehyde is known to be a human carcinogen. That conclu- sion was based on evidence from studies in humans and supporting mechanistic data. The introductory paragraph also informs the reader that formaldehyde was first listed in the 2nd RoC as reasonably anticipated to be a human carcinogen, and that the substance was upgraded to its current listing status of known to be a human carcinogen in the 12th RoC. The committee finds this paragraph to be informative. Cancer Studies in Humans The committee reviewed the “Cancer Studies in Humans” section in the NTP substance profile and the corresponding sections in the background docu- ment. NTP described the search strategy used to identify relevant epidemiologic studies, and the committee judged the choice of substance-specific and topic- specific terms to be reasonable. The committee did not identify any informative epidemiologic studies that were omitted from the background document. The committee judged that the most informative studies were cited by NTP and were appropriately summarized in the substance profile. The distinctions among subtypes of nasopharyngeal and sinonasal cancers were adequately discussed in the background document and in the substance profile. The relevance of the subtypes for the determination of carcinogenicity is appropriately discussed. The evidence in the available literature on which sub- types of nasopharyngeal and sinonasal cancers are increased in incidence by exposure to formaldehyde is modest and not definitive. An increase in incidence that is modest and not definitive is not surprising given the rarity of these tumors and the difficulty of having sufficient statistical power to distinguish patterns of association by subtype of cancer (NTP 2010). The limitation in the literature related to cancer subtypes is appropriately discussed in the substance profile and does not materially limit the validity of the carcinogenicity determination. The committee agrees with NTP’s focus on three principal types of cohort and case–control studies in humans: studies of industrial workers, studies of professional groups that have high exposure (embalmers), and studies of gen- eral-population cohorts and case–control studies. The first two of those provided the most informative evidence because of greater opportunities for exposure of workers and because of higher-quality exposure assessment as a component of the study method. The committee agrees with NTP’s judgment that the two most informative occupational studies for evaluating human cancer hazard posed by formaldehyde are the National Cancer Institute (NCI) study of a cohort of more than 25,000 workers in industries that use formaldehyde (Beane Freeman et al. 2009) and the NCI nested case–control study of cancer in embalmers (Haupt- mann et al. 2009). That judgment was based on the strengths of the studies— 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 35 they are large, high-quality studies that used well-documented methods and high-discrimination exposure assessments. The committee judged the exposure assessments to be of good quality because they included detailed evaluations of the sources and variations in exposure and used appropriate statistical modeling to estimate unmeasured historical exposures (see Appendix C for more discus- sion). Additional strengths of the NCI embalmer study are the likelihood of high exposures for long periods, a well-conducted exposure reconstruction, and a careful analysis of alternative measures of quantitative exposure (Hauptmann et al. 2009). The National Institute for Occupational Safety and Health has produced a mortality study of a cohort of garment workers (Pinkerton et al. 2004). The co- hort was relatively small (2,206 total deaths observed over more than 40 years), and the exposure assessment was less detailed, but the likelihood of substantial exposure before 1970 was clearly documented (Elliot et al. 1987), and the study methods and conduct were rigorous. The study was not informative on the ques- tion of an association between formaldehyde and nasopharyngeal or sinonasal cancers because of low statistical power. If the cohort had experienced the mor- tality rates of the general population in the United States, not even one nasopha- ryngeal cancer death would have been expected in a population of this size. And, consistent with this expectation, no nasopharyngeal cancer deaths were observed. The same is true in this study for sinonasal cancer—less than one death was expected and zero were observed. A British chemical-worker study conducted by Coggon et al. (2003) had a semi-quantitative exposure assessment and was probably also insufficiently powered to determine whether nasopharyn- geal carcinoma or sinonasal carcinoma is associated with formaldehyde expo- sure. NTP considered several population-based case–control studies to be par- ticularly valuable in the assessment of carcinogenicity. The assessment of for- maldehyde exposure and nasopharyngeal cancer was informed by a population– based case–control study by Vaughan et al. (2000) and three smaller case– control studies of nasopharyngeal cancer by Roush et al. (1987), West et al. (1993), and Hildesheim et al. (2001).The assessment of formaldehyde exposure and sinonasal cancer was informed by the pooled case–control studies of sinona- sal cancer reported by Luce et al. (2002) and several smaller case–control stud- ies of sinonasal cancer by Olsen et al. (1984), Hayes et al. (1986), Olsen and Asnaes (1986), Roush et al. (1987), and Luce et al. (1993). Because sinonasal cancers are rare (NTP 2010), it was appropriate for NTP to give substantial weight to the findings from the pooled analysis by Luce et al. (2002) of 12 case– control studies, each of which individually lacked sufficient statistical power to detect an effect. The data from those studies could be combined (pooled) be- cause of common methods of data collection and because a detailed exposure reconstruction was conducted specifically for the pooled analysis. NTP drew on the findings of a meta-analysis by Zhang et al. (2009) and cited meta-analyses by Bachand et al. (2010) and Bosetti et al. (2008). Meta- analyses can be useful in summarizing results of multiple studies, but after re- 

36 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens viewing the published meta-analyses on formaldehyde and evaluating their methodologic differences, the committee decided not to use the published meta- analyses or to conduct its own meta-analysis for its independent assessment of formaldehyde in Chapter 3. Because of the considerable heterogeneity in design, particularly among the exposure assessments, the results of a meta-analysis of the full range of observational studies published on formaldehyde exposure and cancer would be highly sensitive to inclusion and exclusion criteria and to other methodologic decisions (Checkoway et al. 2004). The substance profile described only briefly why Zhang et al. (2009) was given some weight in the assessment of carcinogenicity but Bachand et al. (2010) and Bosetti et al. (2008) were not. Zhang et al. (2009) hypothesized that acute myeloid leukemia (AML) was associated with formaldehyde exposure. The study was unusual in that, unlike some meta-analyses, it had a careful expo- sure rationale for its approach. The authors decided to focus their analyses by using only the highest exposure categories to obtain the strongest test for a rela- tionship between exposure and disease frequency. They assumed that if an in- creased frequency of AML was observed, it would most likely be found by ana- lyzing the contrast between the most highly exposed subjects and the unexposed subjects. They argued that higher relative risks were less susceptible to type 2 errors, higher-exposure categories would be less affected by risk dilution by subjects who had low exposures, and high relative risks were less likely to be a result of confounding factors. They also focused on myeloid leukemia instead of all leukemias because they had hypothesized that AML was causally linked to formaldehyde exposure. In the committee’s own assessment (described in Chap- ter 3), no meta-analyses were considered, because they were not deemed neces- sary in reaching a strong conclusion and because of the difficulties in evaluating conflicting results from different meta-analyses. The committee concluded that NTP did a thorough job of describing the epidemiology literature in the background document and synthesizing infor- mation about key studies in the substance profile. However, the substance pro- file was not transparent about how the epidemiology evidence met the RoC list- ing criteria. The listing criteria indicate that formaldehyde should be categorized as reasonably anticipated to be a human carcinogen if “there is limited evidence of carcinogenicity from studies in humans, which indicates that causal interpre- tation is credible, but that alternative explanations, such as chance, bias, or con- founding factors, could not be adequately excluded” (NTP 2010, p. iv). Formal- dehyde should be categorized as known to be a human carcinogen if “there is sufficient evidence of carcinogenicity from studies in humans, which indicates a causal relationship between exposure to [formaldehyde]…and human cancer” (NTP 2010, p. iv). There was no discussion in the “Cancer Studies in Humans” section of the background document or substance profile about how NTP de- fined the terms limited evidence and sufficient evidence. Therefore, consistent with the RoC listing criteria, the committee used its expert scientific judgment to interpret and apply the listing criteria to the evidence evaluated in Chapters 2 and 3. Limited evidence was defined by the committee as evidence from two or 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 37 more strong or moderately strong studies with varied study designs and popula- tions that suggested an association between exposure to formaldehyde and a specific cancer type, but alternative explanations, such as chance, bias, or con- founding factors, could not be adequately ruled out because of limitations in the studies, and so a causal interpretation could not be accepted with confidence. Sufficient evidence was defined by the committee as consistent evidence from two or more strong or moderately strong studies with varied study designs and populations that found an association between exposure to formaldehyde and a specific cancer type and for which chance, bias, and confounding factors could be ruled out with reasonable confidence because of the study methodologies and the strength of the findings. The way in which the committee categorized studies as strong, moderately strong, or weak is described in more detail in Chapter 3. Nasopharyngeal Cancer As was accurately summarized in the substance profile, nasopharyngeal cancers are a group of uncommon tumors with several histologic types, includ- ing differentiated keratinizing squamous-cell carcinoma, differentiated nonkerat- inizing carcinoma, and undifferentiated nonkeratinizing carcinoma. NTP based its evaluation of epidemiologic evidence of nasopharyngeal cancer on several lines of evidence. The committee reviewed the background document and the findings of a previous expert panel (McMartin et al. 2009) and concurs with the choice of the key studies presented in the substance profile. NTP found several case–control studies to be highly informative, notably a case–control study by Vaughan et al. (2000) that drew incident cases from five US cancer registries that participated in the Surveillance Epidemiology and End Results program of NCI (Vaughan et al. 2000). The committee noted two im- portant contributions of the Vaughan et al. (2000) multicenter case–control study: it was able to evaluate risks separately for the three principal types of nasopharyngeal tumors described above, and the exposure assessment was suffi- ciently detailed to provide evidence of a strong dose–response relationship. Cor- roborating evidence was provided by additional case–control studies by Roush et al. (1987), West et al. (1993), and Hildesheim et al. (2001). The NCI industrial worker cohort also provided important corroborating evidence of an association between formaldehyde exposure and nasopharyngeal- cancer mortality, although the rarity of the tumors limited the statistical power of the study (Hauptmann et al. 2004). The authors observed a pattern of in- creased mortality among categories of exposure defined by duration of expo- sure, average intensity cumulative exposure, and peak exposure. Although the number of cases was not as large, the study was strengthened by its high-quality exposure assessment. The design of the NCI industrial worker cohort consisted of employees in 10 plants. The objective was to obtain a sufficiently large study group to determine causes of increased mortality for common cancers. However, only a small number of nasopharyngeal-cancer deaths occurred. Of the nine 

38 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens deaths, five occurred in workers in a single plant, which was the second largest plant in the study (Hauptmann et al. 2004). As noted by Hauptmann et al. (2005), it is not unusual to see large variation in small numbers of rare cancers across small plants. Two possible explanations for the heterogeneity in out- comes by plant is the heterogeneity in exposures across the plants and the possi- bility of confounding by other carcinogenic exposures in the plant that had the most cases. To evaluate that possibility, the investigators conducted analyses that adjusted for the plant. The results of the adjusted analyses were substantial- ly similar to the unadjusted findings, although limited by the small numbers of cases. Sinonasal Cancer The committee agreed with NTP’s assessment that the Luce et al. (2002) study of sinonasal cancer was particularly useful. As noted, it was a pooled analy- sis of several high-quality case–control studies that shared the same exposure as- sessment, and the resulting statistical power was critical for the study’s findings. The study found a substantial increase in the frequency of one type of sinonasal cancer—adenocarcinoma—after high cumulative exposure to formaldehyde in both men and women. NTP determined that earlier case–control studies by Olsen et al. (1984), Hayes et al. (1986), Olsen and Asnaes (1986), Roush et al. (1987), and Luce et al. (1993) taken as a group provided consistent supporting evidence of an association. The committee found that the issue of potential confounding of the for- maldehyde–sinonasal-cancer association by wood dust was adequately consid- ered by NTP. The substance profile noted that Hansen and Olsen (1995, 1996) were conducted in occupational cohorts in which wood-dust exposure was very unlikely. In addition, several studies either stratified by likely wood-dust expo- sure (Olsen et al. 1984; Hayes et al. 1986; Olsen and Asneas 1986) or fitted models to control for confounding by wood dust statistically (Luce et al. 2002). Although each of the studies taken alone had some limitations because of small numbers of cases, on balance the evidence supports NTP’s conclusion that the observed association between formaldehyde and sinonasal cancer is unlikely to be due to confounding by wood-dust exposure. No other important confounders were identified in the available studies. Lymphohematopoietic Cancer The committee reviewed the background document (NTP 2010) and the findings of the previous expert panel (McMartin et al. 2009) and concurs with the choice of key studies presented under the heading “Lymphohematopoietic Can- cer” in the substance profile (NTP 2011). The committee agrees with NTP that the most informative primary studies for evaluating formaldehyde exposures and lym- phohematopoietic cancers were the NCI study of the cohort of industrial workers 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 39 exposed to formaldehyde (Beane Freeman et al. 2009) and the NCI nested case– control study of embalmers (Hauptmann et al. 2009). As previously mentioned, those studies are informative because of their size and the quality of their design and conduct, particularly because the quality of the extensive exposure assess- ments permitted quantitative evaluations with a variety of plausible exposure met- rics. NTP determined that the most informative studies for evaluating formalde- hyde exposure and myeloid leukemia specifically were the British cohort of industrial workers (Coggon et al. 2003), the NIOSH cohort of garment workers (Pinkerton et al. 2004), the NCI cohort of industrial workers (Beane Freeman et al. 2009), and the NCI nested case–control study of embalmers (Hauptmann et al. 2009). The epidemiology literature is discussed in more detail in Chapter 3. The committee found that the assessment of lymphohematopoietic cancers presented in the substance profile supports NTP’s conclusion that the most strongly supported association is that between myeloid leukemia and formalde- hyde. Broader diagnostic categories (all leukemias and all lymphohematopoietic cancers) also show evidence of an association with formaldehyde exposure in some studies, but a likely explanation for those increases is the inclusion of myeloid leukemia in the broader groupings that include it. The committee agrees with NTP that the evidence demonstrates an association between exposure to high concentrations of formaldehyde (by several different metrics) and some lymphohematopoietic cancers, specifically myeloid leukemia. That association cannot be explained by chance, bias, or confounding factors (NTP 2011). Lymphohematopoietic cancers make up a diverse group that are often ana- lyzed together in epidemiologic studies because of the rarity of the individual types. Concerns have been raised about the usefulness of such a broad category of tumors when evidence of carcinogenicity is being evaluated because the dif- ferent cancers of the hematopoietic system are understood to arise from different cells and so might have different etiologic mechanisms (NRC 2011). There is a common assumption in epidemiology, dating back at least to Bradford Hill (Hill 1965), that specific hazardous exposures, such as exposures to chemicals, tend to cause diseases by a small number of specific pathways (or modes of action), so there is an expectation of observing stronger associations between exposures and narrowly defined disease entities than between exposures and broad catego- ries. Nevertheless, it is common practice in epidemiology to begin an evaluation of exposure–disease associations by looking for signals of an association in broad and heterogeneous groups of diseases (including, for example, the very broad category of all cancers combined or all lung diseases combined). If evi- dence of an association is found in a broad disease category in an exposed popu- lation, the next step is to look into more narrowly defined disease subgroups, such as different types of leukemias. Sometimes, the result is that an association is observed only in the broad group and not in any of the constituent disease subgroups. In such cases, the result is spurious and could possibly be explained by bias in study design or data collection. The more likely explanation, though, is that the association observed in the broad disease category might be accounted for by an increase in the association of one or a small number of specific disease 

40 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens entities when the rest of the broad group shows no increase in the association. The latter pattern is interpreted by the study authors as evidence of an associa- tion between the exposure and the specific subgroup or subgroups of the disease. Cancer at Other Tissue Sites The substance profile discusses cancer at other sites only briefly, so the committee’s assessment of this section is based on the review in the background document (which is also brief but more informative) and a review of some of the primary literature. The committee concurred with NTP’s assessment that the literature published by June 10, 2011, does not meet the requirement of limited evidence of a carcinogenic effect at any additional sites. As stated in the back- ground document, “in general, the reported estimates were null [relative risk = 1.0] or slightly elevated but statistically nonsignificant, and studies have not consistently reported an elevated risk in cancer associated with formaldehyde exposure at any of these sites” (NTP 2010, p. 232). Conclusions Regarding Epidemiologic Evidence The committee concurs with NTP that there is sufficient evidence in stud- ies that had adequate characterization of relevant exposure metrics to enable a conclusion about human cancer after exposure to formaldehyde. The strongest studies are ones that had high-quality exposure assessments and ones that pre- sented alternative exposure metrics. As noted above, there are several such stud- ies. NTP’s discussions of chance, bias, confounding factors, and other limita- tions of the most informative studies in the substance profile are clear and thorough. The committee agrees with NTP’s determination that the human evi- dence published by June 10, 2011, on the association of exposure to formalde- hyde with cancer of the nasopharyngeal region and sinonasal cavities and of myeloid leukemia was sufficient to support a listing as known to be a human carcinogen. Cancer Studies in Experimental Animals The section “Cancer Studies in Experimental Animals” in the substance profile discusses the degree of certainty of the carcinogenicity of formaldehyde on the basis of evidence from experimental animal studies. According to the NTP listing criteria (Box 1-2), evidence from animal studies is to be judged suf- ficient to categorize a chemical as reasonably anticipated to be a human carcino- gen if “there is increased incidence of malignant and/or a combination of malig- nant and benign tumors in multiple species or multiple tissue sites; by multiple routes of exposure; or to an unusual degree with regard to incidence, site, or type of tumor, or age at onset” (NTP 2010, p. iv). The committee reviewed the sub- stance profile in the context of those criteria. 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 41 Neither the formaldehyde substance profile (NTP 2011) nor the back- ground document (NTP 2010) present details of the approach taken to search the literature for animal carcinogenicity studies although a good description of the literature-search strategy was provided by NTP in response to committee inquiry (Bucher 2013; see Table 2-1). The committee reviewed the comprehensive compilation of animal bioassays in the US Public Health Service 149 series Sur- vey of Compounds Which Have Been Tested for Carcinogenicity and evaluations by the International Agency for Research on Cancer (IARC 1982, 1995, 2006), but it did not find other important or informative animal carcinogenesis studies that were missed by NTP and should have been included in the background doc- ument or in the substance profile. It found a few early studies of low power (small numbers of animals were used), of poor quality, or of short duration that were not described in the background document. Examples include a 6-month lung exposure study in rabbits that found atypical proliferation (Garschin and Schabad 1936), a study with no controls that administered formaldehyde to 10 rats via subcutaneous injection and found injection-site sarcomas in four (Watanabe et al. 1954), and a 10-month oral experiment in six rabbits that found intraepithelial carcinoma in the exposed mucosa in two (Muller et al. 1978). Those studies contribute little evidence on formaldehyde carcinogenicity, and the RoC and background document are not remiss or deficient for not evaluating them. Inhalation In the “Inhalation” section of the formaldehyde background document, studies are grouped by species. Two studies discussed in the background docu- ment used mice. The study by Horton et al. (1963) focused on the lung and did not examine the nasal epithelium. C3H mice were exposed to formaldehyde at 0.05 mg/L (50 mg/m3) for 35 weeks and then for 29 weeks of repeated formal- dehyde exposure to 0.15 mg/L (150 mg/m3), for a total of 64 weeks, and then all mice were sacrificed. None of the mice were found to develop pulmonary neo- plasms. The committee judged that this omission from the background docu- ment was appropriate given the severe limitations of the study. Furthermore, the study was not noted in the animal-evidence section of the substance profile and, given the limitations of the study, NTP was reasonable to exclude it from further consideration. Kerns et al. (1983a) conducted a 2-year study of male and female B6C3F1 mice with relatively large dose groups, interim sacrifices (at 6, 12, 18, and 24 months), adequate statistical evaluation, and thorough histopathologic examina- tion of the nasal turbinates and other components of the respiratory tract. Nasal lesions of increasing severity with increasing dose were reported, and two of 17 surviving males in the highest-dose group had squamous-cell carcinoma (Kerns et al. 1983b). The two squamous-cell carcinomas were attributed to formalde- hyde given the rareness of the tumors (the background document reported no 

42 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens tumors of this type in 2,800 historical control animals from NTP studies) and the similarity of the lesions observed in rats by the same authors. The substance profile cited that as evidence of carcinogenicity in male mice, and the committee finds this reasonable. The discussion of the studies in rats in the background document groups the studies as “subchronic” and “chronic”. The subchronic-exposure studies (Rusch et al. 1983; Woutersen et al. 1987; Wilmer et al. 1989) might have been more appropriately placed in a section on “other relevant data” that discussed proliferative lesions. The proliferative lesions observed in the short-term studies (for example, squamous-cell metaplasia and hyperplasia of the nasal epithelium) were observed to precede squamous-cell carcinoma in the chronic studies. How- ever, the short-term studies were of insufficient duration to produce tumors and are not themselves carcinogenesis studies. Their exclusion from the substance profile discussion of animal carcinogenesis is appropriate. The subchronic study by Feron et al. (1988) exposed male Wistar rats to formaldehyde for 13 weeks and then sacrificed the animals after an additional 118 weeks. The 118-week followup period allowed sufficient time for the ef- fects of the 13-week exposure to be manifested. The background document not- ed the variety of nonneoplastic changes in the olfactory epithelium in addition to the nasal tumors observed (polypoid adenoma, squamous-cell carcinoma, and carcinoma in situ). The fact that tumors developed after short-term exposure was appropriately noted in the substance profile. The discussion of the chronic rat studies in the background document be- gins with the large multidose studies in male and female Fischer 344 (F344) rats sponsored by the Chemical Industry Institute of Toxicology (Swenberg et al. 1980a,b; Kerns et al. 1983a). The studies were considered to be state-of-the-art for the time; the methods included a large group, multiple interim sacrifice times, and full histopathologic evaluation of nasal tissue for characterization of neoplastic and nonneoplastic lesions. The studies were well described in the background document. The finding of a high incidence of rare nasal tumors in male and female rats provides a logical and definitive basis for NTP’s conclu- sion on formaldehyde-induced nasal carcinogenesis. The background document cited additional long-term inhalation- carcinogenesis studies in rats. Woutersen et al. (1989) evaluated the effects of damage to the nasal epithelium in male Wistar rats. During the first week of the study, the nasal mucosa of some rats was severely damaged by electrocoagula- tion. A higher nasal-tumor incidence was observed in exposed rats that had damaged nasal epithelium than in rats that had undamaged nasal epithelium, although the study of rats with undamaged epithelium had smaller groups (this was not noted in the background document). Monticello et al. (1996) reported on the relationship between indexes of cell proliferation and induction of nasal tu- mors in relatively large groups (90–147) of male F344 rats that were exposed to a range of concentrations (0.7–15 ppm for 6 hours/day, 5 days/week) for up to 2 years. Squamous-cell carcinoma and polypoid adenoma of the nasal cavity were again found. Kamata et al. (1997) exposed smaller groups of male F344 rats (32 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 43 per group), performed histopathologic evaluations of respiratory tract and non– respiratory tract tissue, and similarly found squamous-cell carcinoma of the na- sal cavity but no cancers at other sites. Sellakumar et al. (1985) studied the ef- fects of formaldehyde in male Sprague Dawley rats and performed a histopatho- logic evaluation of other major tissues; the study did not appear to include bone marrow. Nasal squamous-cell carcinoma was found at a relatively high inci- dence (38% in the group dosed with formaldehyde at approximately 15 ppm). The studies were each adequately described in the background document and reported in the substance profile as providing evidence of formaldehyde-induced carcinogenicity in the nasal epithelium. The committee agrees with the inclusion of the studies because they support the overall sufficiency of evidence of car- cinogenicity in animals exposed to formaldehyde. One chronic study in female Sprague Dawley rats was not cited in the sub- stance profile and was discounted in the background document because of small groups (Holmström et al. 1989). Squamous-cell metaplasia was observed, but only one animal developed nasal squamous-cell carcinoma. The study authors concluded that the finding in the one animal was related to formaldehyde expo- sure, but NTP did not include that as supportive in the substance profile—a rea- sonable decision given the observation of a single tumor. Two monkey studies presented in the background document’s table of na- sal-tumor results were too short to be reported with other carcinogenesis studies, especially in such long-lived animals. One study was in cynomolgus monkeys and was 26 weeks long (Rusch et al. 1983), and the other study was in rhesus monkeys and was only 6 weeks long (Monticello et al. 1989). The limitation regarding study length was not noted in the study description in the background document but was noted in the summary table of carcinogenicity results. It would have been more appropriate not to include those studies in the section on cancer-bioassay data. They were not mentioned in the substance profile, and that is appropriate. Two inhalation studies in Syrian golden hamsters are discussed in the background document. One was only 26 weeks in duration, included a small group size (10 male and 10 female), and resulted in no significant findings (Ru- sch et al. 1983). The background document reported that the study was of short exposure duration and used a small number of animals. The study was not noted in the substance profile and, because it was not a carcinogenesis study, that is appropriate. The study was insufficient as a carcinogenesis study, and NTP would not have been faulted if it had left it out of the background document. The second inhalation study exposed two groups of Syrian golden hamsters over a lifetime (Dalbey 1982). One group (n=88) was exposed 5 hours/day, 5 days/week at 10 ppm, and the second group (n=50) was exposed 5 hours/day, 1 day/week at 30 ppm. Higher incidences of nasal metaplasia and hyperplasia were observed in the 10-ppm group than in the 132 control animals, but no nasal tumors were present. The substance profile did not include the study as a basis of its finding of sufficient evidence for carcinogenesis, and that is appropriate. 

44 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens Oral The background document describes studies in which relatively high con- centrations of formaldehyde were administered to rats in drinking water. In the first study described, eight of 10 Wistar rats that received 5,000 ppm of formalin in drinking water developed squamous-cell papilloma of the forestomach com- pared to none of 10 control animals (Takahashi et al. 1986). The finding is noted in the substance profile, and the committee finds that appropriate. Two other drinking-water studies in Wistar rats (Til et al. 1989; Tobe et al. 1989) found epithelial hyperplasia and hyper keratosis of the forestomach and hyperplasia of the glandular stomach, but no statistically significant differences in tumors be- tween the treated and control animals. One of the studies (Til et al. 1989), which had a reasonable size (70 animals/group), exposed male and female rats for up to 2 years to average concentrations of 20, 260, and 1,900 ppm in drinking water. Tobe et al. (1989) designed a 2-year study with concentrations of formaldehyde in drinking water at 0, 200, 1,000, and 5,000 ppm and group sizes of 20 animals of each sex. None of the high-dose animals survived to the end of the study. The background document describes well the series of drinking-water ex- periments conducted by Soffritti et al. (1989, 2002) in male and female Sprague Dawley rats. Soffritti et al. (1989) exposed animals in utero (dams exposed via drinking water) and postnatally for 2 years. Breeders were exposed for a life- time. In the female offspring, the incidence of malignant intestinal tumors was significantly increased. In a statistical analysis of the study, IARC (2006) found that the incidence of intestinal leiomyosarcoma was significantly increased in female offspring and in male and female offspring combined. The substance profile noted that benign and malignant gastrointestinal tumors were reported, including rare intestinal leiomyosarcomas in females. Because leiomyosarcoma is rare, even with the low incidence NTP deemed the finding significant; this is similar to the IARC (2006) conclusion. The substance profile includes the find- ing and, although the finding is not robust, it is not unreasonable for NTP to include it. In the second series of studies by Soffritti et al. (2002), rats were ex- posed as adults, and males in the high-dose group were observed to have gastro- intestinal leiomyosarcomas, and females in the high-dose group were observed to have leiomyomas. This second finding of gastrointestinal leiomyosarcoma was again given weight because of the rarity of the tumor. In those studies, an increased incidence of hemolymphoreticular tumors was observed, but the find- ing was not given much weight, because of large discrepancies between the ini- tial incidence reported in a preliminary report and the final published incidence, because of pooling of lymphomas and leukemias, and because limited infor- mation was given on the tumor incidence in historical controls. Soffritti et al. (2002) also reported significant increases in tumors of the mammary gland, but the significance did not persist when liposarcomas were removed from the group. The committee agrees with not giving weight to the hemolymphoreticular and mammary tumors in the substance profile and with attaching some weight to the leiomyosarcomas. 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 45 Coexposure with Other Substances The substance profile notes that formaldehyde promotes tumors of the stomach and lung in rats and cites the background document as a reference. There were nine coexposure carcinogenicity studies of varied study design. The results of some studies were null. NTP did not include any of the studies in its findings on the sufficiency of the evidence in animals. That scientific judgment is consistent with the NTP criteria. Conclusion Regarding Animal Evidence NTP concluded that the experimental evidence was sufficient to find that formaldehyde is an animal carcinogen. With regard to NTP’s application of its criteria, it noted that formaldehyde caused “tumors in two rodent species, at sev- eral different tissue sites, and by two different routes of exposure” (NTP 2011, p. 197). A positive finding on any one of the three conditions listed below in which malignant or combined malignant and benign tumors occur would fulfill the criteria for sufficiency in animals. NTP found that two were met. 1. In multiple species or multiple tissue types:  Multiple species: NTP cites studies that showed increases in malig- nant tumors in rats (Feron et al. 1988; Kerns et al. 1983a; Sella- kumar et al. 1985; Soffritti et al. 1989; Woutersen et al. 1989; Mon- ticello et al. 1996; Kamata et al. 1997) and in mice (Kerns et al. 1983a).  Multiple tissue types: NTP cites studies that showed malignancies of the nasal epithelium (mostly squamous-cell carcinomas) (Kerns et al. 1983a; Sellakumar et al. 1985; Feron et al. 1988; Woutersen et al. 1989; Monticello et al. 1996; Kamata et al. 1997) and gastrointesti- nal tract (leiomyosarcoma) (Soffritti et al. 1989 [offspring]; Soffritti et al. 2002 [adults]). The substance profile also noted that benign testicular adenoma was seen in the Soffritti et al. (2002) study. 2. After exposure by multiple routes: NTP cites exposure by inhalation (Kerns et al. 1983a; Sellakumar et al. 1985; Woutersen et al. 1987; Feron et al. 1988; Monticello et al. 1996; Kamata et al. 1997) and oral routes (Soffritti et al. 1989 [offspring]; Soffritti et al. 2002). 3. To an unusual degree with respect to incidence, site, type of tumor, or age at onset: NTP did not state that this criterion was met; however, nasal tu- mors are rarely increased in animal studies, and these tumors were observed at relatively high incidences in the formaldehyde animal studies (Kerns et al. 1983a; Monticello et al. 1996). The committee agrees with NTP’s conclusion that there is sufficient evi- dence of carcinogenicity in animals to support a listing in the 12th RoC. 

46 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens Other Relevant Data The section “Other Relevant Data” of the substance profile presents a se- lection of studies that deal with formaldehyde and the following topics: chemi- cal reactivity, toxicity (in vivo and in vitro), systemic and organ-specific effects, genomic effects (mutagenic), covalent adducts (protein and DNA), carcinogen- icity of formaldehyde metabolites and related compounds, and absorption, dis- tribution, metabolism, and kinetics. Many of the studies are referred to in detail in other sections of the substance profile. The text in this section succinctly and appropriately describes the current understanding of the regional respiratory- tract absorption of formaldehyde and provides appropriate literature citations. The text also accurately describes the reactivity of formaldehyde with water and biologic molecules and accurately indicates the short plasma half-life of formal- dehyde. Biomarkers of formaldehyde’s interaction with macromolecules (blood proteins and DNA adducts) are well documented. The current understanding of the cytotoxicity of formaldehyde is adequately covered. Studies on Mechanisms of Carcinogenesis The section “Studies on Mechanisms of Carcinogenesis” in the substance profile and the associated sections in the background document describe the scientific evidence and mechanistic knowledge available on the carcinogenicity of formaldehyde. The committee finds that the extent, quality, and interpretation of the mechanistic evidence described in these documents are comprehensive and that the importance of this information for the decision to list formaldehyde as a known human carcinogen is clearly explained. Neither the background document nor the substance profile explicitly de- scribes the literature-search strategy; however, as previously stated, the collec- tion of search terms and other information were available on request from NTP (Bucher 2013). On the basis of this information and the content of the back- ground document and the substance profile, the committee concludes that NTP performed a thorough search and appropriately evaluated studies on mechanisms of carcinogenesis that were published in peer-reviewed sources. The committee concludes that the information presented in the background document and the substance profile is comprehensive, balanced, and inclusive and is accompanied by informative evidence tables and short narratives of individual studies. Sum- maries were written in a clear manner, and the limitations of the individual stud- ies, where appropriate, are acknowledged and taken into consideration. The mechanistic information provided critical evidence that demonstrates the plausi- bility of formaldehyde-induced carcinogenesis in both experimental animals and humans. Although there was no clear cutoff date for inclusion of the additional mechanistic studies in the peer-reviewed literature between the time of comple- tion of the background document (November 2009) and the final release of the 12th RoC, the committee concludes that NTP did not miss any publications that 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 47 had strong mechanistic evidence that would have caused NTP to change the listing of formaldehyde as a known human carcinogen. (See Chapter 3 and Ap- pendix D for more information on the committee’s literature search beginning in 2009.) The substance profile focuses on the mechanisms related to specific clini- cal sites of cancers, specifically, nasopharyngeal, sinonasal, and lymphohemato- poietic cancers. The committee finds that delineation of the available mechanis- tic evidence into portal-of-entry or systemic effects as defined by NRC (2011) would have made the background document and the substance profile stronger. The mechanisms of carcinogenicity of highly reactive chemicals, including for- maldehyde, can differ between portal-of-entry sites and distal sites that their native forms or metabolites might not readily reach. Although there are short- comings of the evidence described in the section “Cancer at Other Tissue Sites” as acknowledged by NTP, the mechanistic evidence pertaining to the systemic effects of formaldehyde would probably be applicable to any distal tissues. The committee concludes that NTP correctly states that “the mechanisms by which formaldehyde causes cancer are not completely understood” (NTP 2011, p. 198). There may be several mechanisms of action involved and the mechanisms proposed by NTP are not mutually exclusive and might be related. Although it is clear that the overall strength of evidence differs between the por- tal-of-entry and systemic health effects, most of the evidence presented in the introductory paragraph in this section focuses on a genotoxic mode of action (NTP 2011). An expert panel that reviewed a draft version of the background document stated that two mechanisms are supported by available evidence in sinonasal–pharyngeal regions where inhaled formaldehyde first comes into con- tact with the mucous layer of the respiratory tract in mammals (McMartin et al. 2009): a cytotoxicity-induced cellular-proliferation mechanism and a genotoxic mechanism. The information presented in this section appropriately details stud- ies in model organisms and cell-culture systems that provide general evidence applicable to a wide array of human tissues. Nasal Cancer Most of the upper aerodigestive tract1 is directly exposed to formaldehyde when it is inhaled. Various anatomic structures in this region have been identi- fied as potential sites of formaldehyde-associated carcinogenesis in both exper- imental animals and humans (NTP 2010). This section in the substance profile and the corresponding parts of the background document are comprehensive and 1 The aerodigestive tract is “the combined organs and tissues of the respira- tory tract and the upper part of the digestive tracts (including the lips, mouth, tongue, nose, throat, vocal cords, and part of the esophagus and windpipe)” (NCI 2014). 

48 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens balanced. The committee finds that the information presented in the substance profile agrees with that presented in the background document. Nomenclature of the exact anatomic structures affected by exposure to formaldehyde is important and the section would be clearer if the title reflected the two distinct anatomic sites that have been identified as potential portal-of-entry target sites of formal- dehyde carcinogenesis in humans: the nasopharyngeal and sinonasal regions. Although the emphasis on the various forms of genetic damage observed in the nasal tissue is warranted and the description is comprehensive, the sub- stance profile could have provided a stronger summary of the genotoxic mode of action of formaldehyde in the anatomic sites that come into direct contact with formaldehyde. For example, the nasal passages and surrounding anatomic sites in the upper respiratory tract are affected in rodents (which are obligatory nose- breathers) and humans. However, the oral cavity (for example, the buccal epi- thelium in exposed humans, who might breathe primarily through the mouth because of irritating effects of formaldehyde on the nasal epithelium) and upper digestive tract (in rodent gavage studies) are also target tissues that come into direct contact with formaldehyde. There is mechanistic evidence of adverse health effects of formaldehyde in those anatomic regions (NTP 2010). The substance profile identifies several types of genetic damage that have been observed in exposed humans and animal models. They include DNA– protein cross-links, DNA cross-links, nucleotide base adducts and mutations, and micronuclei. Although the description of genetic damage in the substance profile mentioned key findings and cited appropriate references, the topic would benefit from a clear structure and a clear presentation of the evidence similar to the structure and presentation of evidence in the background document. That could be achieved with a tiered presentation of the information, from damage at the level of a nucleotide (for example, adducts and mutations) to that at the level of the DNA structure (for example, cross-links) or chromatin (for example, mi- cronuclei). By focusing on the types of damage and pointing to whether evi- dence supporting or refuting each type is available from in vitro or ex vivo, ani- mal, or human studies, the substance profile could provide an even more concise and structured description of the plausibility of this mechanism. Cytotoxicity-induced cellular proliferation is identified as a second plausi- ble mechanism of carcinogenicity of formaldehyde at the portal-of-entry sites. The substance profile presented evidence from studies in rodents that histo- pathologic lesions in the upper respiratory tract lead to cell proliferation. The committee finds the description and analysis of those studies to be robust and well presented. The substance profile also appropriately points out that several concentration–response studies identified strong concordance between cytotoxi- city and proliferation (in subchronic studies) and nasal-tumor incidence (in chronic studies) in rodents. The substance profile acknowledges that cytotoxicity-induced cellular pro- liferation has been observed “at anatomical sites that are not thought to be the origin of squamous cell carcinoma” (NTP 2011, p. 199). Although it is not en- tirely clear what anatomic sites are being referred to here, this subsection cor- 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 49 rectly points out that this mechanism is not exclusively responsible for formal- dehyde’s carcinogenicity in the upper respiratory tract, inasmuch as a variety of compounds that alone might induce cell proliferation are known not to pose a cancer hazard in the upper respiratory tract. Those compounds include glutaral- dehyde, chlorine, and ethylacrylate (Miller et al. 1985; Wolf et al. 1995; NTP 1999). The mechanistic studies of the genotoxicity and cytotoxicity of formalde- hyde and the later studies of compensatory cell proliferation and apoptosis in the upper aerodigestive tract in rodents have reported effects at concentrations that are within an order of magnitude of human exposures reported in several occu- pational studies. Whereas few studies involving human subjects have examined cytotoxicity-induced cellular proliferation after exposure to formaldehyde, stud- ies performed with rodent models provide strong mechanistic support for the listing of formaldehyde as a known human carcinogen. Leukemia The section “Leukemia” in the substance profile focuses on the systemic effects of formaldehyde at distal sites and specifically on myeloid leukemia. The committee points out that the issue of nomenclature of the anatomic structures affected by exposure to formaldehyde is important, and the section would be clearer if the title was revised to make it clear that the information in it pertains to systemic effects of formaldehyde. Overall, the substance profile and background document provide a com- prehensive and balanced presentation of the evidence pertinent to the effects of formaldehyde at distal sites. It also properly acknowledges the limitations in the current scientific understanding of the mechanisms associated with the plausibil- ity that formaldehyde causes malignancies of the hematopoietic system. The committee finds that the information presented in the substance profile is in agreement with that presented in the background document. The section “Leukemia” of the substance profile addresses three main is- sues: the cellular origin of myeloid leukemia, the lack of evidence of systemic distribution of formaldehyde or its metabolites, and a general description of sev- eral plausible mechanisms. A brief discussion of the cellular origins of myeloid leukemia frames the challenge that formaldehyde does not seem to reach the bone marrow, where most known leukemogens have been shown to affect hema- topoietic progenitor cells. However, there might be indirect mechanisms by which formaldehyde affects bone marrow and circulating cells (see Chapter 3). The committee finds this logic to be reasonable. The substance profile acknowl- edges that there is little evidence that formaldehyde or its metabolites would reach systemic circulation or tissues other than those in direct contact with the agent. Several key studies have evaluated blood concentrations of formaldehyde after exposure of humans and laboratory animals but found no measurable in- creases (Heck et al. 1985; Casanova et al. 1988; Heck and Casanova 2004). And 

50 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens a study in rats that used 13C-labeled formaldehyde and evaluated DNA-adduct formation in the nasal epithelium and distal anatomical sites, including the bone marrow, was also acknowledged in the substance profile (but not in the back- ground document) to support the assertion that there is an apparent lack of sys- temic distribution of inhaled formaldehyde (Lu et al. 2010). One additional study (Moeller et al. 2011) that examined the presence of formaldehyde- associated endogenous and exogenous N2-hydroxymethyl-dG adducts in nasal mucosa and bone marrow DNA of cynomolgus macaques exposed to 13C- labeled formaldehyde was published within months of the release of the 12th RoC and was not referred to in the substance profile. The committee finds that the information presented in the study was consistent with the evidence present- ed by Lu et al. (2010) and the arguments that were already laid out in the sub- stance profile; inclusion of the new publication in the 12th RoC would not have changed the overall conclusions. Given the uncertainties in the scientific understanding of the potential mechanisms of the systemic effects of formaldehyde, the committee finds that NTP could have explicitly acknowledged, as stated in a previous expert panel’s report (McMartin et al. 2009), that “while it would be desirable to have an ac- cepted mechanism that fully explains the association between formaldehyde exposure and distal cancers, the lack of such mechanism should not detract from the strength of the epidemiological evidence that formaldehyde causes myeloid leukemia” (p. 28). Systemic Effects Observed after Inhalation or Oral Exposure The section “Systemic Effects Observed after Inhalation or Oral Expo- sure” in the substance profile describes several additional lines of evidence that support the notion that formaldehyde has systemic adverse health effects. Such evidence includes data demonstrating toxicity, genotoxicity, and increased inci- dence of malignancies at distal sites (NTP 2011) following inhalation of formal- dehyde. This section in the substance profile and the corresponding parts of the background document are comprehensive and balanced. The committee finds that the information presented in the substance profile agrees with that presented in the background document. Studies presented in this section are highly in- formative and argue that although it is yet to be established how formaldehyde can exert adverse effects systemically, the strongest evidence of a systemic ef- fect of formaldehyde is evidence of genotoxicity in blood cells that circulate beyond the portal of entry. The committee concludes that the study by Lu et al. (2010) and other sup- porting studies strongly argue for the lack of systemic distribution of inhaled formaldehyde. However, it also concludes that the relevance of formaldehyde- induced DNA adducts to formaldehyde-induced carcinogenesis is uncertain giv- en that the background concentrations of these adducts formed by endogenous exposure to formaldehyde are greater than those induced by exogenous formal- 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 51 dehyde at carcinogenic doses, and that tissue concentrations of the adducts vary within and among species tested. In that regard, the committee highlights a point from a previous expert panel’s report that chromosome aberrations are an im- portant biomarker of human cancer (McMartin et al. 2009). The chromosomal aberrations observed in lymphocytes of exposed human subjects constitute strong evidence of potentially genotoxic effects of formaldehyde in circulating blood cells. As acknowledged in the substance profile, evidence of genotoxicity of formaldehyde is extensive. Studies that successfully detected DNA–protein cross-links, strand breaks, micronuclei, and chromosomal aberrations in the cir- culating blood cells of exposed human subjects are convincing and reproducible. No one study performed with human subjects can establish that formaldehyde is the sole genotoxic agent that caused the observed effects, but the diversity of studies, populations, and exposure scenarios gives strong credence to the overall conclusion. Studies of such effects in experimental animals are less consistent, and the substance profile rightly states that “most [experimental animal] studies found no cytogenetic effects” (NTP 2011, p. 199). The background document and substance profile also note that toxicity of formaldehyde has been reported to occur in the liver, testes, central nervous sys- tem, and other organs that would suggest a systemic effect. The publications that were evaluated by NTP include case reports of humans who ingested formalde- hyde, reports of epidemiologic studies of occupational cohorts, and reports of in vivo exposures of experimental animals (rats and mice) of varied duration and dosage. Although the evidence presented in those studies is diverse and credible, NTP correctly states that “the mechanisms for systemic toxicity…are not known” (NTP 2011, p. 199). Theoretical Mechanisms for the Distribution of Formaldehyde to Distal Sites The substance profile accurately describes the theoretical possibility that formaldehyde might diffuse through nasal epithelia to the bloodstream and then throughout the body. The section also provides appropriate literature citations for the information that is presented. Clearly expressed is the salient issue that because of the reversible nature of formaldehyde’s reaction with water (which forms methanediol) or macromolecules, it is theoretically possible that a formal- dehyde or methanediol molecule might move throughout the body. Moreover, as appropriately noted in the background document, mathematical simulation mod- eling efforts that incorporate formaldehyde–methanediol kinetics suggest that formaldehyde might penetrate to the bloodstream in the nose (Georgieva et al. 2003); this raises the possibility that inhaled formaldehyde might reach the sys- temic circulation. The section “Theoretical Mechanisms for Distribution to Distal Sites” of the substance profile is narrowly focused. Although it is theoretically possible that formaldehyde might distribute away from the portal of entry to distant tis- sues, the evaluation in the substance profile would be more complete if the po- 

52 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens tential for formaldehyde to move throughout the body were discussed in the context of the large amounts of endogenous formaldehyde that are present. Such an evaluation would broaden the discussion from one of the theoretical possibil- ity of systemic distribution to a more precise evaluation of whether it is likely to occur to any important extent. Published data that were not cited in this section of the substance profile indicate that inhaled formaldehyde does not increase blood formaldehyde to concentrations that are substantially above endogenous concentrations (Heck et al. 1985; Casanova et al. 1988; Lu et al. 2010; Moeller et al. 2011). Moreover, large amounts of formaldehyde have not been shown to penetrate to tissues distant from the portal of entry. See the detailed toxicokinet- ics discussion in Chapter 3. Other Potential Mechanisms of Formaldehyde-Induced Leukemia The section “Other Potential Mechanisms of Formaldehyde-Induced Leu- kemia” in the substance profile offers two additional potential mechanisms to explain formaldehyde-induced leukemia. The first suggested mechanism is that “formaldehyde could damage stem cells circulating in the blood, which travel to the bone and become initiated leukemia cells,” and the second is that formalde- hyde “could damage stem cells that reside in the nasal turbinates or olfactory mucosa” (NTP 2011, pp. 199-200). Both mechanisms are related to potential direct damage to hematopoietic stem cells in the nasal circulation or nasal muco- sa. Literature was cited to support the implicit hypothesis that formaldehyde- induced damage occurs to hematopoietic stem cells at the portal of entry. How- ever, this hypothesis has not been proved experimentally (reported data are re- lated to formaldehyde-induced damage in lymphocytes, not stem cells, in circu- lation or in nasal mucosa). Thus, this section might appear to provide evidence to support the listing (even using the term support twice) although it simply suggests some feasibility of the mechanisms. In the absence of direct evidence, these potential mechanisms do not explain how formaldehyde causes leukemia. Supporting and critical literature are mentioned appropriately in the back- ground document and substance profile. Because this section does not bear on the listing of formaldehyde and because there is no direct evidence of the mech- anisms, the review of the literature and the discussion are appropriately brief. Hematotoxicity In the section “Hematotoxicity” of the substance profile, NTP reviews ev- idence of formaldehyde-induced hematologic effects (NTP 2011). The term hematotoxicity might imply a health effect that is not addressed in the studies cited in the substance profile. Indeed, the studies presented in the listing profile demonstrate changes in blood-cell number or function but do not address wheth- er the changes have consequences for the health of the animal or human (for example, autoimmunity, infection, bleeding, or leukemia). 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 53 The substance profile cites two studies that support the hypothesis that formaldehyde induces hematologic effects. Substantial space is given to Zhang et al. (2010), who investigated occupational exposure to formaldehyde, hemato- toxicity, and leukemia-specific chromosomal changes in cultured myeloid pro- genitor cells. However, several others studies cited in the background document could also contribute to this topic in the substance profile. For example, Ying et al. (1999) investigated lymphocyte subsets and sister-chromatid exchanges in students exposed to formaldehyde vapor. The authors established some speci- ficity of the hematologic effects of formaldehyde, so citing their study in the substance profile would have strengthened the discussion in this section. Some balance is achieved in the first two sentences of the section in the substance pro- file although no clear synthesis of the evidence is presented. Because a number of studies provide direct and indirect evidence relevant to this topic, a balanced summary sentence on the overall weight of evidence would be helpful. It is im- portant to note that observed changes in hematopoietic cell number or function do not directly support a mechanism of leukemogenesis but rather establish that formaldehyde has effects either directly or indirectly on hematopoietic cells in the circulation. For clarity, it should be stated how this section affects NTP’s listing of formaldehyde as a carcinogen. PROPERTIES The section “Properties” of the substance profile details major physicochem- ical characteristics of formaldehyde. Chemical stability, reactivity, and flammabil- ity characteristics are also provided. Overall, this brief section serves its purpose well and provides all necessary information on the chemical itself. The section also includes information on various alternative states of formaldehyde, including a monomeric hydrate methylene glycol (methanediol) form of formaldehyde in dilute aqueous solutions, a solid form (1,3,5-trioxane), and various polymers of eight to 100 formaldehyde units that form paraformaldehyde. USE The section “Use” of the substance profile and related background docu- ment provide a comprehensive review of industrial uses of formaldehyde and paraformaldehyde. Formaldehyde is used primarily in the production of polymer products and resins, so humans might come into contact with formaldehyde through a variety of consumer products and manufacturing processes. Overall, this section supports well the reasoning for considering inclusion of formalde- hyde in the RoC in that it is clear that “a significant number of persons residing in the United State are exposed” (NTP 2010, p. 3) to this chemical. 

54 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens PRODUCTION The section “Production” of the substance profile covers the chemical pro- cesses used to manufacture formaldehyde and provides quantitative estimates of domestic production and of import and export volumes. Formaldehyde is a high- volume production chemical, and manufacturing of this compound is increasing. This section and corresponding information from the background document supports a potential wide exposure to formaldehyde in the United States, inas- much as about 30 lb of formaldehyde was produced per person in the United States in the middle 2000s. Much of that formaldehyde is used to manufacture a wide variety of products and it enters the market as a component of industrial resins, building materials, home and office furnishings, mortuary chemicals and preservatives, disinfectants in farming, and consumer products. Substantial quantities are also produced from natural sources and combustion sources. This section supports the inclusion of formaldehyde in the RoC. EXPOSURE The goal of the section “Exposure” in the substance profile is to show that there is widespread occupational and general population exposure. The section is divided into two subsections: environmental exposures and occupational ex- posures. The section on “Human Exposure” in the background document has a subsection on “Biological Indices of Exposure”. That subsection is brief and does not consider effects of endogenous formaldehyde formation, which will limit the utility of a biomarker because the variation in endogenous formalde- hyde will obscure the small signal produced by exogenous exposure. However, it seems to show that some biomarkers distinguish between exposed and nonex- posed workers when the exposure is high enough. The committee observed that the purpose of the section “Exposure” in the background document was not to critically evaluate the industrial exposures that were present for epidemiologic studies evaluated in the section “Cancer Studies in Humans”. Instead, it catalogs the highly heterogeneous data gathered in stud- ies of a wide array of environmental and occupational exposure settings and establishes that substantial occupational exposures and widespread exposures of the general population occur. REGULATIONS AND GUIDELINES The “Regulations” and “Guidelines” sections of the substance profile pro- vides a comprehensive list of various rules, regulations, and advisory notices that pertain to formaldehyde. It is clear that many government agencies in the United States have set quantitative limits of exposure in various scenarios and regulate production, use, distribution, and disposal of formaldehyde, but the 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 55 level of detail provided on these in the background document and substance profile varies widely, and it is not clear in many cases whether the appropriate source can be easily found. Many regulations are dated without links to the ap- propriate document sources. REVIEW OF NTP’S LITERATURE-SEARCH METHODS NTP conducted several literature searches to identify carcinogenicity stud- ies that inform the assessment of formaldehyde in the NTP 12th RoC, and some of that information is presented in the section “Human Cancer Studies” of the background document (NTP 2010). For that specific section in the background document, NTP identified some of its search terms, the databases searched, and the inclusion and exclusion criteria that were used. Such details were not includ- ed in the background document for other topics, including studies in experi- mental animals and mechanistic data. In response to a request from the committee, NTP provided additional in- formation on its literature search methods (Bucher 2013). PubMed, Scopus, and Web of Science were searched by using substance-specific terms (that is, the substance name, major synonyms, and major metabolites) and topic-specific terms (see Table 2-1). The results underwent a first level of review, during which titles and abstracts were screened for relevance, followed by a second level of review in which the full text of references was reviewed for relevance and substance. In the second level of review, 1,170 references were considered. Some 38 additional references were recommended to NTP by an expert panel (McMartin et al. 2009, 2010). In total, 798 references were cited in the final background document. The date when the searches were run and the specific search strings used for each database were not provided to the committee. The committee found that including more detail on the search strategies and on the inclusion and exclusion criteria would have improved transparency of the meth- ods that NTP used to identify and evaluate relevant scientific literature related to formaldehyde exposure and carcinogenicity. Other committees of the National Academies (IOM 2011; NRC 2011, 2014) have made related recommendations about clearly and concisely describing literature searches, and approaches that ensure greater transparency in literature searches and systematic reviews are being initiated by the US Environmental Protection Agency’s Integrated Risk Information System (EPA 2013) and NTP’s Office of Health Assessment and Translation (NTP 2013). The final background document summarizes the literature up to the date of the peer review of the background document (November 2009), and the sub- stance profile includes literature up to the date of the peer review by the NTP Board of Scientific Counselors (June 2010) (Bucher et al. 2013). (see Figure 1-1 

56 TABLE 2-1 Topic-Specific Search Terms Used in NTP’s Database Searches Human Cancer Animal Tumors Genotoxicity ADME and Mechanisms MeSH terms MeSH terms MeSH terms MeSH terms Case reports Adenocarcinoma Aneuploidy Absorption Case–control studies Adenoma Cell transformation, Biotransformation Cohort studies Carcinogens neoplastic Metabolism Epidemiology Carcinoma Chromosome aberrations Pharmacokinetics Epidemiologic studies Neoplasms Cytogenic analysis Cytochrome P-450 enzyme system Mortality Precancerous condition DNA adducts Neoplasms Sarcoma DNA damage Text words Occupational exposure Animals DNA repair Activation Prospective studies Germ-line mutation Bioactivation Retrospective studies Text words Micronuclei Clearance Manpower Cancer Mutagens Detoxif* Foci Mutagenesis Distribution Text words Malignan* Mutation Excretion Case-referent Mice Oncogenes Kinetics Cancer Oncogenic* Polyploidy Mechanism Carcinogenic Rats Sister chromatid exchange Metabolite Epidemiolog* Tumor SOS response Tumor Tumorigenic* Workers Text words Chromosom* Clastogen* Genetic toxicology Strand break Unscheduled DNA synthesis *The asterisk, sometimes referred to as a “wildcard”, represents a truncation and it is used to find all terms that begin with the given text string. Abbreviations: ADME, absorption, distribution, metabolism, and excretion; MeSH, medical subject headings. Source: Bucher 2013. 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 57 for a schematic of the 12th RoC process.) NTP periodically reviewed the scien- tific literature up to the release of the 12th RoC (June 2011) “for any new stud- ies that would warrant a re-review of the NTP’s preliminary recommendations to the HHS Secretary for the listing status of formaldehyde” (Bucher 2013). De- scribing that process in greater detail in the background document, including specific dates, would have added transparency to the development of the back- ground document and substance profile. SUGGESTED REVISIONS FOR FUTURE EDITIONS OF THE FORMALDEHYDE LISTING IN THE REPORT ON CARGINOGENS Through its review of the background document and substance profile for formaldehyde, the committee identified several revisions that could be made to improve the formaldehyde listing in future iterations of the RoC (see Table 2-2). Addressing the suggestions in Table 2-2 would add clarity and improve the presentation of information in NTP’s assessment of formaldehyde, but making the revisions would not change the overall conclusion of carcinogenicity pre- sented in the substance profile. SUMMARY AND CONCLUSIONS In response to the statement of task, the committee examined the sub- stance profile published by NTP as part of the 12th RoC. It also examined sup- porting documents, including those presented in Table 1-1, and relevant primary literature. The committee considered information presented in review articles, reviews completed by such scientific bodies as IARC, and materials submitted to it by the public. The committee found that the background document describes the strengths and weaknesses of relevant studies in a way that is consistent and bal- anced. The substance profile appropriately cites studies showing positive associ- ations that support the listing. However, the substance profile would be more complete if it included more discussion on why weaker, uninformative, incon- sistent, or conflicting evidence did not alter NTP’s conclusions. Although the committee identified that as a limitation in the substance profile, it would not change NTP’s final conclusions as presented in the substance profile. The committee concludes that NTP comprehensively considered available evidence and applied the listing criteria appropriately in reaching its conclusion. The 12th RoC states that “formaldehyde is known to be a human carcinogen based on sufficient evidence of carcinogenicity from studies in humans and sup- porting data on mechanisms of carcinogenesis” (NTP 2011, p. 195). The com- mittee agrees with NTP’s conclusion, which is based on evidence published by June 10, 2011, that formaldehyde is a known human carcinogen. 

58 TABLE 2-2 Suggested Revisions for the Formaldehyde Substance Profile and Background Document In Future Editions of the Report on Carcinogens Sections in the Substance Profile for Formaldehyde Suggested Revisions Study Identification  Describe the process for identifying relevant literature (including databases searched, keywords used, and search dates). Cancer Studies in Humans  Explicitly define the way in which RoC listing criteria terms such as limited and sufficient were used in the evaluation of the human studies.  Clarify how the quality and relevance of meta-analyses were evaluated and how and why meta-analyses were included in the assessment of the epidemiology evidence.  Add a more detailed description of how exposure assessments were used to evaluate the evidence from individual epidemiology studies.  Include an explanation of the logic used to decide which tumor groupings or end points to include in evaluating epidemiologic evidence. Cancer Studies in Experimental Animals  Consider including a finding that formaldehyde induces tumors to an unusual degree (high incidences of rare squamous-cell tumors of the nasal epithelium). Other Relevant Data  Include a description of the portal-of-entry toxicity of formaldehyde.  Add a discussion in the background document for formaldehyde of the extensive metabolism of formaldehyde at the portal of entry.  Add a discussion of formaldehyde as a well-established irritant that has the potential to produce an allergic response. Studies on Mechanisms of Carcinogenesis Nasal Cancer  Change the title of the section on “Nasal Cancer” to reflect the two distinct potential portal-of-entry target sites.  Strengthen the summary of the genotoxic mode of action discussion.  Restructure the discussion in the substance profile to parallel the presentation of information in the background document. 

Leukemia  Change the title of the section on “Leukemia” to make it clear that the information pertains to potential systemic effects of formaldehyde.  Explicitly acknowledge that “while it would be desirable to have an accepted mechanism that fully explains the association between formaldehyde exposure and distal cancers, the lack of such mechanism should not detract from the strength of the epidemiological evidence that formaldehyde causes myeloid leukemia” (McMartin et al. 2009).  Discuss the potential for formaldehyde to move throughout the body in the context of the large amounts of endogenous formaldehyde that are present.  Make it clear that the section on “Other Potential Mechanisms of Formaldehyde-induced Leukemia” is intended to show feasibility, not evidence of or support for the mechanisms.  Change the title of the section “Hematotoxicity” to “Hematologic and Immunologic Effects” so that the substance profile is consistent with the background document. In addition, add a balanced summary sentence to that section on the overall strength of the evidence and state how that section affects NTP’s listing for formaldehyde as a carcinogen. Exposure  Integrate information from the section “Exposure” about environmental and occupational settings into the assessment of the epidemiologic studies in the “Human Studies” section.  Strengthen and focus the listing of heterogeneous data in the background document by removing any incomplete and limited data and by providing a more organized presentation of the information.  Compare and contrast different types of industries in a quantitative manner. Situations that involve exposure to particulate materials that contain formaldehyde could be treated separately. Occupational and other activities that produce peak exposures could also be noted and measured. Time trends, if any, in exposure could be identified.  Adopt a consistent unit of exposure for occupational and environmental exposures. Regulations and Guidelines  Provide more information on regulations and include proper references to the sources. 59 

60 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens REFERENCES Bachand, A.M., K.A. Mundt, D.J. Mundt, and R.R. Montgomerty. 2010. Epidemiological studies of formaldehyde exposure and risk of leukemia and nasopharyngeal cancer: A meta-analysis. 40(2):85-100. Beane Freeman, L.E., A. Blair, J.H. Lubin, P.A. Stewart, R.B. Hayes, R.N. Hoover, and M. Hauptmann. 2009. Mortality from lymphohematopoietic malignancies among workers in formaldehyde industries: The National Cancer Institute Cohort. J. Natl. Cancer Inst. 101(10):751-761. Bosetti, C., J.K. McLaughlin, R.E. Tarone, E. Pira, and C. La Vecchia. 2008. Formalde- hyde and cancer risk: A quantitative review of cohort studies through 2006. Ann. Oncol. 19(1):29-43. Bucher, J.R. 2013. Follow-up Questions. Material submitted by the NAS Committee on Review of the Formaldehyde Assessment in the NTP 12th RoC and the NAS Committee on Review of the Styrene Assessment in the NTP 12th RoC, April 2, 2013. Casanova, M., H.D. Heck, J.I. Everitt, W.W. Harrington Jr., and J.A. Popp. 1988. For- maldehyde concentrations in the blood of rhesus monkeys after inhalation expo- sure. Food Chem. Toxicol. 26(8):715-716. Checkoway, H., N. Pearce, and D. Kribel. 2004. Research Methods in Occupational Epi- demiology, 2nd Ed. Oxford: Oxford University Press. Coggon, D., E.C. Harris, J. Poole, and K.T. Palmer. 2003. Extended follow-up of a cohort of British chemical workers exposed to formaldehyde. J. Natl. Cancer Inst. 95(21):1608-1615. Dalbey, W.E. 1982. Formaldehyde and tumors in hamster respiratory tract. Toxicology 24(1):9-14. Elliot, L.J., L.T. Stayner, L.M. Blade, W. Helperin, and R. Keenlyside. 1987. Formaldehyde Exposure Characterization in Garment Manufacturing Plants: A Composite Sum- mary of Three in-depth Industrial Hygiene Surveys. Division of Surveillance, Hazard Evaluations and Field Studies, National Institute for Occupational Safety and Health, Cincinnati, OH. EPA (U.S. Environmental Protection Agency). 2013. Part 1. Status of Implementation of Recommendations. Materials Submitted to the National Research Council, by In- tegrated Risk Information System Program, U.S. Environmental Protection Agen- cy, January 30, 2013 [online]. Available: http://www.epa.gov/iris/pdfs/IRIS%20 Program%20Materials%20to%20NRC_Part%201.pdf [accessed Jan. 13, 2014]. Feron, V.J., J.P. Bruyntjes, R.A. Woutersen, H.R. Immel, and L.M. Appelman. 1988. Nasal tymours in rats after short-term exposure to a cytotoxic concentration of formaldehyde. Cancer Lett. 39(1):101-111. Garschin, W.G., and L.M. Schabad. 1936. About atypical proliferation of the bronchial epithelium with the introduction of formalin into the lung tissue [in German]. Z. Krebsforsch. 43(1):137-145. Georgieva, A.V., J.S. Kimbell, and P.M. Schlosser. 2003. A distributed-parameter model for formaldehyde update and disposition in the rat nasal lining. Inhal. Toxicol. 15(14):1435-1463. Hansen, J., and J.H. Olsen. 1995. Formaldehyde and cancer morbidity among male em- ployees in Denmark. Cancer Causes Control 6(4):354-360. Hansen, J., and J.H. Olsen. 1996. Occupational exposure to formaldehyde and risk of cancer [in Danish]. Ugeskr. Laeger. 158(29):4191-4194. 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 61 Hauptmann, M., J.H. Lubin, P.A. Stewart, R.B. Hayes, and A. Blair. 2004. Mortality from solid cancers among workers in formaldehyde industries. Am. J. Epidemiol. 159(12):1117-1130. Hauptmann, M., J.H. Lubin, P.A. Stewart, R.B. Hayes, and A. Blair. 2005. Re: Mortality from Solid Cancers among Workers in Formaldehyde Industries. The Authors Re- ply. Am. J. Epidemiol. 161(11):1090-1091. Hauptmann, M., P.A. Stewart, J.H. Lubin, L.E. Beane Freeman, R.W. Hornung, R.F. Herrick, R.N Hoover, J.F. Fraumeni Jr., A. Blair, and R.B. Hayes. 2009. Mortality from lymphohematopoietic malignancies and brain cancer among embalmers ex- posed to formaldehyde. J. Natl. Cancer Inst. 101(24):1696-1708. Hayes, R.B., J.W. Raatgever, A. de Bruyn, and M. Gerin. 1986. Cancer of the nasal cavi- ty and paranasal sinuses, and formaldehyde exposure. Int. J. Cancer 37(4):487- 492. Heck, H.D., and M. Casanova. 2004. The implausibility of leukemia induction by for- maldehyde: A critical review of the biological evidence on distant-site toxicity. Regul. Toxicol. Pharmacol. 40(2)92-106. Heck, H.D., M. Casanova-Schmitz, P.B. Dodd, E.N. Schachter, T.J. Witek, and T. Tosun. 1985. Formaldehyde (CH2O) concentrations in the blood of humans and Fischer- 344 rats exposed to CH2O under controlled conditions. Am. Ind. Hyg. Assoc. J. 46(1):1-3. Hildesheim, A., M. Dosemeci, C.C. Chan, C.J. Chen, Y.J. Cheng, M.M. Hsu, I.H. Chen, B.F. Mittl, B. Sun, P.H. Levine, J.Y. Chen, L.A. Brinton, and C.S. Yang. 2001. Occupational exposure to wood, formaldehyde, and solvents and risk of nasopha- ryngeal carcinoma. Cancer Epidemiol. Biomarkers Prev. 10(11):1145-1153. Hill, A.B. 1965. The environment and disease: Association or causation? Proc. R. Soc. Med. 58(5):295-300. Holmström, M., B. Wilhelmosson, and H. Hellquist. 1989. Histological changes in the nasal mucosa in rats after long-term exposure to formaldehyde and wood dust. Ac- ta Otolaryngol. 108(3-4):274-283. Horton, A.W., R. Tye, and K.L. Stemmer. 1963. Experimental carcinogenesis of the lung. Inhalation of gaseous formaldehyde or an aerosol coal tar by C3H mice. J. Natl. Cancer Inst. 30:31-43. IARC (International Agency for Research on Cancer). 1982. Chemicals, Industrial Pro- cesses and Industries Associated with Cancer in Humans: An Updating of IARC Monographs Volumes 1 to 29. IARC Monographs on the Evaluation of the Car- cinogenic Risks to Humans Supplement 4. Lyon, France: IARC [online]. Availa- ble: http://monographs.iarc.fr/ENG/Monographs/suppl4/Suppl4.pdf [accessed June 10, 2013]. IARC (International Agency for Research on Cancer). 1995. Wood Dust and Formalde- hyde. IARC Monographs on the Evaluation of the Carcinogenic Risks to Humans Vol. 62. Lyon, France: IARC [online]. Available: http://monographs.iarc.fr/ENG/ Monographs/vol62/mono62.pdf [accessed June 10, 2013]. IARC (International Agency for Research on Cancer). 2006. Formaldehyde, 2- Butoxyethanol and 1-tert-Butoxy-propan-2-ol. IARC Monographs on the Evaluation of the Carcinogenic Risks to Humans Vol. 88. Lyon, France: IARC [online]. Availa- ble: http://monographs.iarc.fr/ENG/Monographs/vol88/mono88.pdf [accessed June 10, 2013] IOM (Institute of Medicine). 2011. Finding What Works in Health Care: Standards for Systematic Reviews. Washington, DC: National Academies Press. 

62 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens Kamata, E., M. Nakadate, O. Uchida, Y. Ogawa, S. Suzuki, T. Kaneko, M. Saito, and Y. Jurokawa. 1997. Results of a 28-month chronic inhalation toxicity study of for- maldehyde in male Fisher-344 rats. J. Toxicol. Sci. 22(3):239-254. Kerns, W.D., K.L. Pavkov, D.J. Donofrio, E.J. Gralla, and J.A. Swenberg. 1983a. Car- cinogenicity of formaldehyde in rats and mice after long-term inhalation exposure. Cancer Res. 43(9):4382-4392. Kerns, W.D., D.D. Donofrio, and K.L. Pavkov. 1983b. The chronic effects of formalde- hyde inhalation in rats and mice: A preliminary report. Pp. 111-131 in Formalde- hyde Toxicity, J.E. Gibson, ed. Washington, DC: Hemisphere Publishing. Lu, K., L. Collins, H. Ru, E. Bermudez, and J. Swenberg. 2010. Distribution of DNA adducts caused by inhaled formaldehyde is consistent with induction of nasal car- cinoma but not leukemia. Toxicol. Sci. 116(2):441-451. Luce, D., M. Gerin, A. Leclerc, J.F. Morcet, J. Brugere, and M. Goldberg. 1993. Sinona- sal cancer and occupational exposure to formaldehyde and other substances. Int. J. Cancer. 53(2):224-231. Luce, D., A. Leclerc, D. Begin, P.A. Demers, M. Gerin, E. Orlowski, M. Kogevinas, S. Belli, I. Bugel, U. Bolm-Audorff, L.A., Brinton, P. Comba, L. Hardell, R.B. Hayes, C. Magnani, E. Merler, S. Preston-Martin, T.L. Vaughan, W. Zheng, and P. Boffetta. 2002. Sinonasal cancer and occupational exposures: A pooled analysis of 12 case-control studies. Cancer Causes Control 13(2):147-157. McMartin, K.E., F. Akbar-Khanzadeh, G.A. Boorman, A. DeRoos, P. Demers, L. Peter- son, S.M. Rappaport, D.B. Richardson, W.T. Sanderson, and M.S. Sandy. 2009. Part B – Recommendation for Listing Status for Formaldehyde and Scientific Jus- tification for the Recommendation. Formaldehyde Expert Panel Report [online]. Available: http://ntp.niehs.nih.gov/ntp/roc/twelfth/2009/November/FA_PartB.pdf [accessed July 17, 2013]. McMartin, K.E., F. Akbar-Khanzadeh, G.A. Boorman, A. DeRoos, P. Demers, L. Peter- son, S.M. Rappaport, D.B. Richardson, W.T. Sanderson, and M.S. Sandy. 2010. Part A – Peer Review of the Draft Background Document on Formaldehyde. For- maldehyde Expert Panel Report [online]. Available: http://ntp.niehs.nih.gov/ ntp/roc/twelfth/2009/november/fa_parta.pdf [accessed July 17, 2013]. Miller, R.R., J.T. Young, R.J. Kociba, D.G. Keyes, K.M. Bodner, L.L. Calhoun, and J.A. Ayres. 1985. Chronic toxicity and oncogenicity bioassay of inhaled ethyl acrylate in Fischer 344 rats and B6C3F1 mice. Drug Chem. Toxicol. 8(1-2):1-42. Moeller, B.C., K. Lu, M. Doyle-Eisele, J. McDonald, A. Gigliotti, and J.A. Swenberg. 2011. Determination of N2-hydroxymethyl-dG adducts in the nasal epithelium and bone marrow of nonhuman primates following 13CD2-formaldehyde inhalation exposure. Chem. Res. Toxicol. 24(2):162-164. Monticello, T.M., K.T. Morgan, J.I. Everitt, and J.A. Popp. 1989. Effects of formalde- hyde gas on the respiratory tract of rhesus monkeys. Pathology and cell prolifera- tion.. Am. J. Pathol. 134(3):515-527. Monticello, T.M., J.A. Swenberg, E.A. Gross, J.R. Leininger, J.S. Kimbell, S. Seilkop, T.B. Starr, J.E. Gibson, and K.T. Morgan. 1996. Correlation of regional and non- linear formaldehyde-induced nasal cancer with proliferating populations of cells. Cancer Res. 56(5):1012-1022. Muller, P., G. Raabe, and D. Schumann. 1978. Leukoplakia induced by repeated deposi- tion of folmalin in rabbit oral mucosa. Long –term experiments with a new ‘oral tank”. Exp. Pathol. 16(1-6):36-42. NCI (National Cancer Institute). 2014. NCI Dictionary of Cancer Terms [online]. Availa- ble: http://www.cancer.gov/dictionary?cdrid=44811 [accessed April 21, 2014]. 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 63 NRC (National Research Council). 2011. Review of the Environmental Protection Agen- cy’s Draft IRIS Assessment of Formaldehyde. Washington, DC: National Acade- mies Press. NRC (National Research Council). 2014. Review of EPA’s Integrated Risk Information System (IRIS) Process. Washington, DC: National Academies Press. NTP (National Toxicology Program). 1999. NTP Technical Report on the Toxicology and Carcinogenesis Studies of Glutaraldehyde (CAS No. 111-30-8) in F344/N Rats and B6C3F1 Mice (Inhalation Studies). NTP TR 490. U.S. Department of Health and Human Services, Public Health Service, National Institute of Health, National Toxicology Program, Research Triangle Park, NC [online]. Available: http://ntp.niehs.nih.gov/ntp/htdocs/LT_rpts/tr490.pdf [accessed July 17, 2013]. NTP (National Toxicology Program). 2010. Report on Carcinogens Background Docu- ment for Formaldehyde, January 22, 2010. U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program, Research Triangle Park, NC [online]. Available: http://ntp.niehs.nih.gov/ntp/roc/twelfth/2009/Novem ber/Formaldehyde_BD_Final.pdf [accessed July 17, 2013]. NTP (National Toxicology Program). 2011. Formaldehyde. Pp. 195-205 in Report on Carcinogens, 12th Ed. U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program, Research Triangle Park, NC [online]. Available: http://ntp.niehs.nih.gov/ntp/roc/twelfth/profiles/formaldehyde. pdf [accessed July 17, 2013]. NTP (National Toxicology Program). 2013. Draft OHAT Approach for Systematic Re- view and Evidence Integration for Literature-Based Health Assessments. U.S. De- partment of Health and Human Services, National Institute of Health, National In- stitute of Environmental Health Sciences, Division of National Toxicology Program, Office of Hazard Assessment and Translation, February 2013 [online]. Available: http://ntp.niehs.nih.gov/NTP/OHAT/EvaluationProcess/DraftOHATAp proach_February2013.pdf [accessed July 17, 2013]. Olsen, J.H., and S. Asnaes. 1986. Formaldehyde and the risk of squamous cell carcinoma of the sinonasal cavities. Br. J. Ind. Med. 43(11):769-774. Olsen, J.H., S.P. Jensen, M. Hink, K. Faurbo, N.O. Breum, and O.M. Jensen. 1984. Oc- cupational formaldehyde exposure and increased nasal cancer risk in man. Int. J. Cancer 34(5):639-644. Pinkerton, L.E., M.J. Hein, and L.T. Stayner. 2004. Mortality among a cohort of garment workers exposed to formaldehyde: An update. Occup. Environ. Med. 61(3):193- 200. Roush, G.C., J. Walrath, L.T. Stayner, S.A. Kaplan, J.T. Flannery, and A. Blair. 1987. Nasopharyngeal cancer, sinonasal cancer, and occupations related to formalde- hyde: A case-control study. J. Natl. Cancer Inst. 79(6):1221-1224. Rusch, G.M., J.J. Clary, W.E. Rinehart, and H.F. Bolte. 1983. A 26-week inhalation tox- icity study with formaldehyde in the monkey, rat, and hamster. Toxicol. Appl. Pharmacol. 68(3):329-343. Sellakumar, A.R., C.A. Snyder, J.J. Solomon, and R.E. Albert. 1985. Carcinogenicity of formaldehyde and hydrogen chloride in rats. Toxicol. Appl. Pharmacol. 81(3 Pt 1):401-406. Soffritti, M., C. Maltoni, F. Maffei, and R. Biagi. 1989. Formaldehyde: An experimental multipotential carcinogen. Toxicol. Ind. Health 5(5):699-730. Soffritti, M. F. Belpoggi, L. Lambertin, M. Lauriola, M. Padovani, and C. Maltoni. 2002. Results of long-term exposreimental studies on the carcinogeneicity of formalde- hyde and acetaldehyde in rats. Ann. N.Y. Acad. Sci. 982:87-105. 

64 Review of the Formaldehyde Assessment in the NTP 12th Report on Carcinogens Swenberg, J.A., W.D. Kerns, R.I. Mitchell, E.J. Gralla, and K.L. Pavkov. 1980a. Induc- tion of squamous cell carcinomas of the rat nasal cavity by inhalation exposure to formaldehyde vapor. Cancer Res. 40(9):3398-3402. Swenberg, J., W. Kerns, K. Pavkov, R. Mitchell, and E.J. Gralla. 1980b. Carcinogenicity of formaldehyde vapor: Interim findings in a long-term bioassay of rats and mice. Pp. 283-286 in Mechanisms of Toxicity and Hazard Evaluation: Proceedings of the Second International Congress on Toxicology, July 6-11, 1980, Brussels, Belgium, B. Holmstedt, R. Lauwerys, M. Mercier, and M. Roberfroids, eds. Amsterdam: Elsevier North-Holland Biomedical Press. Takahashi, M., R. Hasegawa, F. Furukawa, K. Toyoda, H. Sato, and Y. Hayashi. 1986. Effects of ethanol, potassium metabisulfite, formaldehyde and hydrogen peroxide on gastric carcinogenesis in rats after initiation with N-methyl-N'-nitro-N- nitrosoguanidine. Jpn J. Cancer Res. 77(2):118-124. Til, H.P., R.A. Woutersen, V.J. Feron, V.H. Hollanders, H.E. Falke, and J.J. Clary. 1989. Two-year drinking-water study of formaldehyde in rats. Food Chem. Toxicol. 27(2): 77-87. Tobe, M., K. Naito, and Y. Kurokawa. 1989. Chronic toxicity study on formaldehyde administered orally to rats. Toxicology 56(1):79-86. Vaughan, T.L., P.A. Stewart, K. Teschke, C.F. Lynch, G.M. Swanson, J.L. Lyon, and M. Berwick. 2000. Occupational exposure to formaldehyde and wood dust and naso- pharyngeal carcinoma. Occup. Environ. Med. 57(6):376-384. Watanabe, F., T. Matsunaga, T. Soejima, and Y. Iwata. 1954. Study of the carcinogenici- ty of aldehyde. 1. Experimentally produced rat sarcomas by repeated injections of aqueous solution of formaldehyde [in Japanese]. Gan. 45(2-3):451-452. West, S., A. Hildesheim, and M. Dosemerci. 1993. Non-viral risk factors for nasopharyn- geal carcinoma in the Philippines: Results from a case-control study. Int. J. Cancer 55(5):722-727. Wilmer, J.W., R.A. Woutersen, L.M. Appelman, W.K. Leeman, and V.J. Feron. 1989. Subchronic (13-week) inhalation toxicity study of formaldehyde in male rats: 8- hour intermittent versus 8-hour continuous exposures. Toxicol. Lett. 47(3):287- 293. Wolf, D.C., K.T. Morgan, E.A. Gross, C. Barrow, O.R. Moss, R.A. James, and J.A. Popp. 1995. Two-year inhalation exposure of female and male B6C3F1 mice and F344 rats to chlorine gas induces lesions confined to the nose. Fundam. Appl. Tox- icol. 24(1):111-131. Woutersen, R.A., L.M. Appelman, J.W. Wilmer, H.E. Falke, and V.J. Feron. 1987. Sub- chronic (13-week) inhalation toxicity study of formaldehyde in rats. J. Appl. Toxi- col. 7(1):43-49. Woutersen, R.A., A. van Garderen-Hoetmer, J.P. Bruijntjes, A. Zwart, and V.J. Feron. 1989. Nasal tumors in rats after severe injury to the nasal mucosa and prolonged exposure to 10ppm formaldehyde. J. Appl. Toxicol. 9(1):39-46. Ying, C.J., X.L. Ye, H. Xie, W.S. Yan, M.Y. Zhao, T. Xia, and S.Y. Yin. 1999. Lympho- cyte subsets and sister-chromatid exchanges in the students exposed to formalde- hyde vapor. Biomed. Environ. Sci. 12(2):88-94. Zhang, L., C. Steinmaus, D.A. Eastmond, X.K. Xin, and M.T. Smith. 2009. Formalde- hyde exposure and leukemia: A new meta-analysis and potential mechanisms. Mu- tat. Res. 681(2-3):150-168. Zhang, L., X. Tang, N. Rothman, R. Vermeulen, Z. Ji, M. Shen, C. Qiu, W. Guo, S. Liu, B. Reiss, L.B. Freeman, Y. Ge, A.E. Hubbard, M. Hua, A. Blair, N. Galvan, X. Ruan, B.P. Alter, K.X. Xin, S. Li, L.E. Moore, S. Kim, Y. Xie, R.B. Hayes, M. 

Review of the Formaldehyde Profile in the NTP 12th Report on Carcinogens 65 Azuma, M. Hauptmann, J. Xiong, P. Stewart, L. Li, S.M. Rappaport, H. Huang, J.F. Fraumeni Jr., M.T. Smith, and Q. Lan. 2010. Occupational exposure to for- maldehyde, hematotoxicity and leukemia-specific chromosome changes in cul- tured myeloid progenitor cells. Cancer Epidemiol. Biomarkers Prev. 9(1):80-88.