thought to be the most important causes of cancer, although clearly the ulti-mate role of diet in the etiology of cancer is still being unraveled. The next most important group of factors are infection, hormones, background ioniz-ing radiation, occupation, and alcohol. Of relatively less importance are ultraviolet radiation, industrial products, water and air pollution, and food additives, exposures that tend to receive a disproportionate amount of media attention.
One limitation in interpreting Table 6 is that it does not take into account interactions between exposures. For example, smoking increases the risk of lung cancer, as does exposure to asbestos; however, the risk of lung cancer in smokers exposed to asbestos is much greater than expected based on each risk factor considered individually. Other well-established interactions include smoking and radon for lung cancer, smoking and alco-hol for esophageal cancer, and hepatitis B infection and exposure to afla-toxin for liver cancer. Other interactions are likely.
4. Gene–environment interaction. While carcinogen exposure triggers the onset of cancer, a person’s genetic makeup determines how they respond to the exposure. Thus, genes may increase or decrease risk from the expo-sure and so this is considered a gene–environment interaction. There is cur-rently great interest in identifying interactions between genetic and environmental causes of cancer. As alluded to above, most (but by no means all) of the interest is focused on the interaction of susceptibility genes with environmental exposures. Although unknown at this time, much of the 80% of cancer thought to be due to environmental causes may be due to gene–environment interactions (39). The study of gene–environment interactions will consume much of epidemiological research over the next decade.
ACKNOWLEDGMENTS
Dr. Cerhan was supported in part by a Preventive Oncology Academic Award from the National Cancer Institute (K07 CA64220). Technical assis-tance was provided by Sara Butler Osborn, Robert Vierkant, and Mary Jo Janisch.
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