Projected changes in breast cancer incidence due to the trend toward delayed childbearing.

Because there has been a recent trend toward delay of childbearing in the United States, women in the birth cohort of 1945-49 will have an estimated 5 per cent greater incidence of breast cancer, and those in the cohort of 1950-54 an estimated 9 per cent greater incidence compared with the cohort of 1935-39, which had the distribution of age at first birth most favorable for breast cancer risk.