Although cancer is a genetic disease, most cancers are not inherited, and many are influenced by environmental factors. The role of environmental factors in cancer is suggested by differences in the incidence of specific cancers throughout the world (Table 16.2). The results of studies show that migrant populations typically take on the cancer incidence of their host country. For example, the overall rates of cancer are considerably lower in Japan than in Hawaii. However, within a single generation after migration to Hawaii, Japanese people develop cancer at rates similar to those of native Hawaiians. The increased cancer among the migrants is due to the fact that they are exposed to the same environmental factors as the natives are.

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A number of environmental factors contribute to cancer, but those that have the greatest effects include tobacco use, diet, obesity, alcohol, and UV radiation (Table 16.3). Other environmental factors that induce cancer are certain types of chemicals, such as benzene (used as an industrial solvent), benzo[a]pyrene (found in cigarette smoke), and polychlorinated biphenyls (PCBs; used in industrial transformers and capacitors). Most environmental factors associated with cancer cause somatic mutations that stimulate cell division or affect the process of cancer.

Environmental factors may interact with genetic predispositions to cancer. Lung cancer, for example, is clearly associated with smoking, an environmental factor. Genome-wide association studies (see Chapter 15) revealed that variation at several genes predisposes some people to smoking-induced lung cancer. Variants at some of these genes cause people to be more likely to become addicted to smoking. Other predisposing genes encode receptors that bind potential carcinogens in cigarette smoke. TRY PROBLEM 17