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Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam
reviewed. Where studies have focused on cancer in one of the organs included in the GI system, it is noted in the text discussion.
A case-control study was conducted among white male Iowans over age 30 who died of stomach cancer between 1964 and 1978 (Burmeister et al., 1983). A statistically elevated increased risk of stomach cancer was observed for farmers (OR = 1.3). The odds ratio remained significantly increased when the association between birth cohort and age at death was examined. Deaths before 1970 also showed an association (OR = 1.4) with stomach cancer.
A case-control study in Sweden (Hardell, 1981) looked at risk for colon cancer and found no excess risk for agricultural workers or others exposed to phenoxy herbicides. Likewise, a case-control study of colon cancer, following a PMR analysis (PMR = 1.5, CI 1.1-2.0) among forest and soil conservationists (Alavanja et al., 1989) found no elevated risk of colon cancer associated with being a forest (OR = 1.4, CI 0.7-2.8) or soil (OR = 1.2, CI 0.7-2.0) conservationist.
There were many studies that examined one or more gastrointestinal tract cancers where no consistent associations were found. These included studies of chemical production workers in the U.S. and other countries (Lynge, 1985; Coggon et al., 1986; Thomas, 1987; Bond et al., 1988; Zober et al., 1990; Fingerhut et al., 1991; Manz et al., 1991; Saracci et al., 1991), agricultural workers (Burmeister, 1981; Wiklund, 1983; Hoar et al., 1986; Alavanja et al., 1988; Wigle et al., 1990; Hansen et al., 1992; Ronco et al., 1992), pesticide applicators (Axelson et al., 1980; Blair et al., 1983; Swaen et al., 1992), paper and pulp workers (Robinson et al., 1986; Henneberger et al., 1989; Solet et al., 1989), the Seveso population (Bertazzi et al., 1989a,b; Pesatori et al., 1992), other environmental exposure (Lampi et al., 1992), and Vietnam veterans (Kogan and Clapp, 1985; Lawrence et al., 1985; Anderson et al., 1986a,b; Boyle et al., 1987; Breslin et al., 1988).
Results for these cancers are summarized in Tables 8-2 through 8-5. The epidemiologic studies examining stomach cancer, pancreatic cancer, rectal cancer, and colon cancer were evenly distributed around the null. Estimated relative risks were usually near 1.0, and only the rare study in this group found a statistically significant elevated relative risk.
Strength of Evidence in Epidemiologic Studies
There is limited/suggestive evidence of no association between exposure to herbicides* (2,4-D; 2,4,5-T and its contaminant TCDD; cacodylic