Age-specific patterns of association between breast cancer and risk factors in black women, ages 20 to 39 and 40 to 54.

Data from the 1980 to 1982 population-based Cancer and Steroid Hormone case-control study of women 20 to 54 years old afforded the opportunity to investigate risk factors for breast cancer among black women younger than 40 years (177 patients and 137 control subjects) and to compare the results to black women 40 to 54 years old (313 patients and 348 control subjects). Information on exposure variables was obtained by in-person interviews. The logistic regression results indicated that the risk of breast cancer among black women younger than 40 years was nearly three times greater for those who used oral contraceptives for more than 10 years relative to never-users (odds ratio, 2.8; 95% confidence interval, 1.2 to 6.8) and more than four times greater for severely obese women (body mass index > or = 32.30 kg/m2) relative to women whose relative weights were less than 24.90 kg/m2. Patterns of association for the two age groups were similar for surgical menopausal, age at first full-term pregnancy, and multiple births, but differed for age at menarche.