Breast cancer--interaction between ethnicity and environment.

The risk to develop breast cancer varies at least five fold around the world. Migrant women from low incidence countries to the United States experience an increase in risk over several generations. The objectives of this paper are to describe ethnic differences in breast cancer incidence and to review research related to risk factors that may explain these variations. Although ethnic differences can be partially explained by established risk factors, a large proportion of the increase in risk remains unexplained. Hormonal factors, including estrogens, insulin, and growth factors, may offer an explanatory mechanism how increasing caloric intake, decreasing physical activity, changes in nutrients, increasing height, and adiposity affect breast cancer risk. Future research on polymorphisms in genes coding for enzymes that are involved in the chemical activation and detoxification of environmental carcinogens, dietary agents, and endogenous hormones may contribute to the understanding of ethnic differences in breast cancer risk.