The "epidemic" of breast cancer in the U.S.--determining the factors.

Breast cancer incidence rates in the United States rose by 24% between 1973 and 1991. Mortality during this period, however, remained stable. Both the 5-year relative survival rate and the rates of in situ and stage I breast cancers have been increasing, while the incidence of later-stage cancers has been decreasing. Increased mammography screening may explain the documented jump in breast cancer incidence rates during the mid-1980s. Differences in the distribution of breast cancer risk factors may account, in part, for the temporal trends in breast cancer incidence. In particular, breast cancer risk factors may vary by birth cohort, including age at menarche, age at first birth, physical activity, obesity, diet, alcohol intake, estrogen therapy, and exposure to environmental organochlorines. After decades of epidemiologic research, a preventive approach to breast cancer that focuses on the physiologic effects of the sex steroid hormones, and their potential interactions with family history, is being carefully formulated.