Effect of age on incidence of breast cancer in females.

Incidence and mortality data on breast cancer in females from various Occidental (Western) and Japanese populations were analyzed. After adjustment for birth cohort and year of event, the age curves from all the Western populations were very similar in shape. The age curve for Osaka incidence was very similar in shape to the Western incidence curves. The Osaka curve continued to increase after menopause; the postmenopausal decrease in rates in individual cross sections was the result of a strong cohort effect. The premenopausal mortality curve for Japan was very similar in shape to the Western curves; however, the postmenopausal Japanese mortality curve had a smaller slope at each point.