The overall impact of environment in the broadest sense of the term is reflected in the international variation in cancer incidence, with the differential in rates between high to low incidence populations as great as 50 to 150-fold for melanoma and cancers of the nasal pharynx, the prostate and the liver. However, even for these tumors, genetic factors associated with ethnicity cannot be discounted. They contribute to the patterns of melanoma that depend on the degree of skin pigmentation as well as sun exposure of the population, and they contribute to the excess of nasal pharyngeal cancer in the Chinese population and to the excess of prostate cancer in African Americans as suggested by recent genome-wide studies.