The outcomes reviewed in this chapter follow a common format. Each section begins by providing some background information about the cancer under discussion, including data concerning its incidence in the general U.S. population. A brief summary of the findings described in the first three Agent Orange reports—Veterans and Agent Orange: Health Effects of Herbicides Used in Vietnam (hereafter referred to as VAO; IOM, 1994), Veterans and Agent Orange: Update 1996 (hereafter, Update 1996; IOM, 1996), and Veterans and Agent Orange: Update 1998 (hereafter, Update 1998; IOM, 1999) —is then presented, followed by a discussion of the most recent scientific literature and a synthesis of the material reviewed. Where appropriate, reviews are separated by the type of exposure (occupational, environmental, Vietnam veteran) being addressed. Each section concludes with the committee’s finding regarding the strength of the evidence in epidemiologic studies, biologic plausibility, and evidence regarding Vietnam veterans.

Expected Number of Cancer Cases Among Vietnam Veterans in the Absence of Any Increase in Risk Due to Herbicide Exposure

To provide some background for the consideration of cancer risks in Vietnam veterans, this chapter also reports information on cancer incidence in the general U.S. population. Incidence rates are reported for individuals between the ages of 45 and 59 because most Vietnam era veterans are in this age group. The data, which were collected as part of the Surveillance, Epidemiology, and End Results (SEER) Program of the National Center for Health Statistics (NCHS), are categorized by sex, age, and race because these factors can have a profound effect on the estimated level of risk. Prostate cancer incidence, for example, is nearly 11 times higher in men age 55–59 than in 45–49-year-olds and more than twice as high in African Americans age 45–59 as in whites of this age group (NCI, 2000). The figures presented for each cancer are estimates for the entire U.S. population, not precise predictions for the Vietnam veteran cohort. It should be remembered that numerous factors may influence the incidence reported here—including personal behavior (e.g., smoking and diet), genetic predisposition, and other risk factors such as medical history. These factors may make a particular individual more or less likely than average to contract a given cancer. Incidence data are reported for all races and also separately for African Americans and whites. The data reported are for 1993–1997, the most recent data available at the time this report was written.

As detailed in Chapter 6, here, and in the following chapters, great uncertainties remain about the magnitude of potential risk from exposure to herbicides and dioxin in the occupational, environmental, and veteran studies reviewed by the committee. Many have inadequate controls for important confounders, and the information needed to extrapolate from the level of exposure in the studies to that of individual Vietnam veterans is lacking. The committee therefore cannot quan-



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