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.
PIP: In this case control study among Black American women, the findings showed that differences in breast cancer risk between Black women aged 20-39 years and Black women aged 40-54 years are related to age at menarche, oral contraceptive use, and family history of breast cancer. An inverse relationship was found with age at menarche and a positive relationship with duration of oral contraceptive use among women 20-39 years. The logistic model with all variables included revealed that increased risk was related to an increasing Body Mass Index (BMI) as an adult, lack of breast feeding under the age of 25 years, and the duration of oral contraceptive use among women aged under 40 years. BMI had a stronger impact among women aged under 40 years when BMI at age 18 years was included. Both age groups showed reduced risk with surgical menopause. The final logistic regressions indicated that younger women with menarche at under the age of 12 years had 50% less breast cancer risk than younger women with menarche at 14 years or older. Severely obese younger women had four times the breast cancer risk as women weighing under 24.90 kg/m squared. For women who used oral contraceptives for 10 years or more, the adjusted odds ratio was 2.8 compared to never-users. This finding was unique. Age at initiation of use was unrelated. Results suggested that older women with a family history of breast cancer or with menarche at 13 years and younger had a higher relative risk; early age at menarche was a protection against breast cancer only among younger women. Breast feeding before the age of 25 years may affect risk of breast cancer among women under 40 years of age. Education was unrelated. The findings indicate the importance of examining within race differences by sociocultural differences and reproductive life style choices. Data were obtained from the CASH study by the Centers for Disease Control on 490 women aged 20-54 years who had been diagnosed with primary breast cancer between December 1, 1980 and December 31, 1982 and 485 controls.