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. A second key issue for herbicide exposure and cancer risks is latency, the effect of timing of exposure on subsequent risk of disease. Chapter 8 addresses this issue in detail.

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 scientific evidence described in the first two Agent Orange reports—Veterans and Agent Orange (1994; hereafter referred to as VAO), and Veterans and Agent Orange: Update 1996 (hereafter, Update 1996)—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.

The Department of Veterans Affairs (DVA) asked the committee to specifically address the classification of chondrosarcomas of the skull as part of its work. This is done in the discussion of bone cancer below.

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 14 times higher in men age 55-59 than in 45-49 year olds and nearly twice as high in African Americans age 45-59 than in whites of this age group (NCI, 1998). 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 the years 1990-1994, the most recent available at the time this report was written.

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