Cohort-specific risks of developing breast cancer to age 85 in Connecticut.

Previous estimates of the lifetime risk of developing breast cancer have used cross-sectional estimates of incidence. Cross-sectional rates, however, yield a biased picture of cohort risks when rates are unstable, as breast cancer trends have been. We developed cohort life tables for Connecticut women born from 1888-1892 to 1948-1952 to generate more specific estimates of breast cancer risk to age 85. Multiple decrement life tables were produced for each birth cohort. We included as cases only the first reports of breast cancer in women with no earlier malignancy. Our results indicate that widely circulated lifetime risks of 1 in 9 may be inflated slightly owing to changing incidence. We estimate that of those women 40-44 years old in 1992, 1 woman in 10 will develop breast cancer by age 85. For women born between 1928 and 1932, 1 in 13 will be diagnosed with breast cancer by age 85. The results are insensitive to mortality trends in the past. Errors in the estimates are more likely to arise from changes in incidence and mortality in the future.