In this chapter, background information about each cancer, including data on its incidence in the general US population, is followed by a brief 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; and Veterans and Agent Orange: Update 2000, hereafter, Update 2000, IOM, 2001), 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, and Vietnam veteran). Each section ends with the committee's conclusion regarding the strength of the evidence from epidemiologic studies, biologic plausibility, and evidence regarding Vietnam veterans.
As mentioned above, data on cancer incidence in the general US population are included in the background sections. Those data provide context for the consideration of cancer risks in Vietnam veterans. Incidences are reported for people 45–59 years old 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 can have a profound effect on risk. Prostatic cancer incidence, for example, is nearly 11 times higher in men 55–59 years old than in men 45–49 years old and more than twice as high in blacks 45–59 years old as in whites in this age group (NCI, 2000). The figures presented for each cancer are estimates for the entire US population, not precise predictions for the Vietnam-veteran cohort. It should be remembered that numerous factors may influence the incidences reported here—including personal behavior (such as smoking and diet), genetic predisposition, and medical history. Those factors may make a particular person more or less likely than the average person to contract a given cancer. Incidence data are reported for all races and also separately for blacks and whites. The data reported are for 1995–1999, the most recent data available at the time this report was written.
Great uncertainties remain about the magnitude of potential risk posed by exposure to herbicides and TCDD in the occupational, environmental, and veteran studies reviewed by the committee. Many of those studies have inadequate controls for important confounders, and the information needed to extrapolate from the exposure in the studies to that of individual Vietnam veterans is lacking. The committee therefore cannot measure the risk likely to have been experienced by Vietnam veterans due to exposure to herbicides in Vietnam; it offers qualitative observations where data permit.
Gastrointestinal tract tumors include some of the most common cancers. The committee reviewed the data on colon cancer (ICD-9 153.0–153.9), rectal cancer