Interpretation of the vital statistics of breast cancer

Examination of cross-sectional and longitudinal age-specific incidence and mortality rates for breast cancer in the United States and selected areas leads to 3 main findings: 1. Breast cancer incidence and mortality rise sharply during the reproductive years, then continue to rise postmenopausally but at a slower rate; 2. Breast cancer incidence prior to age 55 has increased about 45% since 1935, while above age 55 incidence has remained constant; and 3. There are marked racial and regional differences in breast cancer incidence. These facts suggest the hypothesis that the risk from breast cancer is related to the frequency and quality of ovarian function which are, in turn, related to environmental factors. The marked differences in breast cancer frequency between Japanese women and women of other nationalities suggest that genetic factors may also play a role.