Comparative analysis of breast cancer risk factors among African-American women and White women.

The authors assessed risk factor profiles among 1,505 African-American and 1,809 White women in the 1993-2001 Carolina Breast Cancer Study. Multiple logistic regression models for case-control data were used to estimate odds ratios for several factors. Racial differences were observed in the prevalence of many breast cancer risk factors among both younger (aged 20-49 years) and older (aged 50-74 years) women. For older women, the magnitude and direction of associations were generally similar for African-American and White women, but important racial differences were observed among younger women. In particular, multiparity was associated with increased risk of breast cancer among younger African-American women (for three or four pregnancies: adjusted odds ratio (OR) = 1.5, 95% confidence interval (CI): 0.9, 2.6; for five or more pregnancies: OR = 1.4, 95% CI: 0.6, 3.1) but not among younger White women (for three or four pregnancies: OR = 0.7, 95% CI: 0.4, 1.2; for five or more pregnancies: OR = 0.8, 95% CI: 0.2, 3.0). The relations with age at first full-term pregnancy and nulliparity also varied by race. Case-only analyses before and after further adjustment for tumor stage and hormone receptor status revealed little effect on results. Hence, racial variations in both prevalences of and risks associated with particular factors may contribute to the higher incidence of breast cancer among younger African-American women.