cancers, a latency period of 10 years or more may elapse between exposure and the detection of cancer (ACS, 2002a).
Lifestyle factors and environmental or occupational exposures—including smoking, diet, infectious diseases, and exposures to chemicals and radiation—are associated with an estimated three-fourths of all cancer deaths in the United States. On a population level, tobacco use, unhealthy diet, and physical inactivity are more likely to affect cancer risk than are trace amounts of pollutants in food, drinking water, and air. However, the degree of risk posed by pollutants depends on the dose and duration of exposure. For example, workers exposed to high concentrations of ionizing radiation, some chemicals, metals, and other substances have been shown to be at increased risk for cancer (ACS, 2002a).
Cancer is most likely the result of a multifactorial process over a lifetime, so it is difficult to establish definitive causal relationships. When investigating the factor or factors that may contribute to the development of cancer, epidemiologists must address several different issues, including environmental and occupational exposures, past lifetime activities (such as smoking), long latency periods, high fatality rates, and the need for accurate diagnoses; all of these issues are discussed in Chapter 2. Exposure determination, the role of confounding, and other broad epidemiologic issues considered by epidemiologists and the committee in evaluating the studies are also presented in Chapter 2. Issues germane to the cancer literature on exposure to insecticides and the decisions made by the committee in reviewing this literature are discussed below. Issues specific to the cancer literature and solvent exposure are discussed in the introduction of Chapter 6.
The pesticides identified by the US Congress, the Department of Defense, and the Department of Veterans Affairs as potentially being used during the Gulf War were all insecticides except for one insect repellent (N,N-diethyl-3-methylbenzamide [DEET]) (see Appendix D for complete list of insecticides reviewed by the committee). Therefore, the committee focused its review on exposure to insecticides in general, to classes of insecticides, and to specific insecticides. However, the literature on insecticides and cancer outcomes includes studies of occupations or populations—such as farmers, agricultural workers, and pesticide applicators—with exposure to numerous agricultural chemicals including insecticides. Most of those studies focus on exposure to pesticides as a broad group of chemical compounds. The term pesticide is often used in studies when the specific agents are not known or when a mixture of insecticides and other pest-control agents are thought to have been used. Use of pesticides could involve exposure to all types of pest-control agents—including insecticides, herbicides, fungicides, and other agents—and it is not possible to determine whether the reported associations with pesticide exposure are related to the specific insecticides of interest in this report. Most of the studies are occupational and use farmers, agricultural workers, or pesticide applicators as surrogates of exposure to the broad group of chemical agents known as pesticides. As a result, the potential for exposure misclassification bias is a limitation of those studies. The committee did not make conclusions of association on the broad category of pesticides because it includes herbicides, fungicides, and other agents not known to have been used during the Gulf War.
Another limitation of the literature is the small number of study subjects, which is due to the specificity of the exposure and the rarity of individual cancers. Although the