Original Contribution Timing of Menarche and First Full-Term Birth in Relation to Breast Cancer Risk

Ages at menarche and first birth are established risk factors for breast cancer. The interval between these ages may also affect risk, since the breast is more susceptible to carcinogenic insults during this period than during the parous period. However, few investigators have studied this relation. Using logistic regression, the authors eval-uated associations between the timing of reproductive events and breast cancer risk among 4,013 cases and 4,069 controls enrolled in a multicenter, population-based US case-control study of White and African-American women (1994–1998). For White, parous premenopausal and postmenopausal women, those who had an interval of 16 years between the ages of menarche and first birth had 1.5-fold (95 % confidence interval (CI): 1.0, 2.2) and 1.4-fold (95 % CI: 1.1, 1.8) increased risks of breast cancer, respectively, in comparison with those who had 5 year