Socioeconomic status and breast cancer risk in African-American women Free

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High individual and neighborhood socioeconomic status (SES) have been associated with a small increase in the risk of breast cancer in studies of white women. Reasons for the associations are unclear. We investigated SES at the individual level (educational attainment of the participant) and the neighborhood level (neighborhood SES score) in relation to breast cancer incidence in the Black Women’s Health Study (BWHS). The BWHS began in 1995 when 59,000 black women from across the U.S. completed mailed questionnaires. Biennial questionnaires collect updated information on exposures and the occurrence of cancers and other health outcomes. U.S. census data at the block group level were linked to participant addresses for each questionnaire cycle from 1995 to 2003. A composite neighborhood SES score was created using information from six census variables -- median housing value, median household income, % with college education,% white collar, % households headed by a single female, and % with interest and dividends. Cox proportional hazards regression was used to compute incidence rate ratios (IRRs) and 95% confidence intervals (CI). Covariates included in multivariable models as potential intermediates for an association were age at first birth, parity, age at menarche, geographic region, body mass index at age 18, adult height, alcohol consumption, physical activity, oral contraceptive use, and menopausal hormone use. Overall, in analyses of 987 incident breast cancer cases, neither personal education nor neighborhood SES was materially associated with breast cancer risk: the IRR for 16+ years of education relative to 12 or fewer years was 1.12 (CI 0.95-1.32) in age-adjusted analyses and 1.07 (CI 0.88-1.29) in multivariable analyses, and the IRR for highest versus lowest quintile of neighborhood SES score was 1.06 (CI 0.87-1.30) in age-adjusted analyses and 0.98 (CI0.79-1.21) in multivariable analyses. Among women under age 45 (319 breast cancer cases), high individual level of education was associated with increased risk: the IRR for 16+ years relative to less than or equal to 12 years was 1.41 (CI 1.00-1.99) age-adjusted, and 1.44 (CI 0.98-2.12), multivariable. Higher neighborhood SES was not associated with risk among women under 45 and there were no associations with education or neighborhood SES among women aged 45 and older. Results were unchanged when analyses were restricted to women who reported a mammography in the previous two-year period. Our results indicate that neighborhood SES is not an independent risk factor for breast cancer in U.S. black women. This may relate to the fact that neighborhood of residence is not as closely linked to individual socioeconomic factors in black women as in white women. Blacks are more likely than whites to live in low-income neighborhoods even when they have high levels of education and high incomes. The explanation for a positive association of individual educational level with breast cancer risk, observed among young women but not among older women in our study, remains unknown.