In assessing a possible connection between herbicide exposure and risk of cancer, one important issue is the magnitude of exposure for the people included in a study. As noted in Chapter 5, there is a great variety in detail and accuracy of exposure assessment among the studies the committee reviewed. A small number used biologic markers of exposure, such as the presence of a compound in serum or tissues; some developed an index of exposure from employment or activity records; others used surrogate measures of exposure, such as being present when herbicides were used. Inaccurate assessment of exposure can obscure the presence or absence of exposure–disease associations and thus make it less likely that a true risk will be identified.
In this chapter, background information about each cancer, including data on its incidence in the general US population, is followed by a summary of the findings described in the previous Agent Orange reports (Veterans and Agent Orange, hereafter referred to as VAO [IOM, 1994]; Veterans and Agent Orange: Update 1996, hereafter, Update 1996 [IOM, 1996]; Veterans and Agent Orange: Update 1998, hereafter, Update 1998 [IOM, 1999]; Veterans and Agent Orange: Update 2000, hereafter, Update 2000 [IOM, 2001]; and Veterans and Agent Orange: Update 2002, hereafter, Update 2002 [IOM, 2003]), a discussion of the most recent scientific literature, and a synthesis of the material reviewed. Where appropriate, the literature is discussed by exposure type (occupational, environmental, service in Vietnam). Each section ends with the committee’s conclusion regarding the strength of the evidence from epidemiologic studies, biologic plausibility, and evidence regarding epidemiology and Vietnam veterans.
Cancer incidence data for the general US population are included in the background sections to provide a context for consideration of cancer risk in Vietnam veterans. Incidences are reported for people 50–64 years old because most Vietnam-era veterans are in this age group. The data, which were collected for the Surveillance, Epidemiology, and End Results (SEER) Program of the National Institutes of Health—National Cancer Institute, are categorized by sex, age, and race, all of which can have a profound effect on risk. Prostate cancer incidence, for example, is approximately 4.4 times higher in men between the ages of 60 and 64 than it is in men 50–54 years old; it is approximately twice as high in blacks 50–64 years old as it is in whites in the same age group (NCI, 2004). The figures presented for each cancer are estimates for the entire US population, not predictions for the Vietnam-veteran cohort. Many factors can influence incidence, among them personal behavior (tobacco use, diet), genetic predisposition, and medical history. Those factors can make someone more or less likely than average to contract a given cancer. Incidence data are reported for all races and also separately for blacks and whites. The data reported are for 1997–2001, the most recent data set available to the committee.
Incidence figures given here are not directly comparable to the figures listed in earlier Updates. Earlier reports used 1990 US Census data; this report used data from the 2000 Census, so some of the differences in incidence estimates