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The incidence of estrogen receptor positive (ER+) breast cancer is higher among white women relative to black women. In two large prospective cohorts, the Black Women's Health Study (BWHS) and the Nurses' Health Study II (NHSII), we investigated whether reproductive factors explain the difference.During 1,582,083 person-years of follow-up of 140,914 women observed from 1995 to 2007, 327 ER+ breast cancers were identified among black women in BWHS and NHSII and 1,179 among white women in NHSII. Cox proportional hazards regression models, stratified by race and pooled, were used to estimate hazard ratios (HR) and 95 % confidence intervals (CI) for the association of race, parity, age at first birth, and lactation in relation to risk of ER+ cancer with adjustment for age and other breast cancer risk factors.Age at first birth differed markedly in the two groups, with 66 % of parous black women having their first child before age 25 as compared with 36 % of white women. Each additional year of age at first birth was associated with a 4 % increased risk of ER+ breast cancer among both racial groups. Relative to nulliparous women, parous women were at decreased risk of ER+ breast cancer (HR 0.59, 95 % CI 0.20, 1.77), in black women and (HR 0.63, 95 % CI 0.45, 0.87) in white women. The HR for the association of black race with ER+ cancer was 0.67 (95 % CI 0.53, 0.84) in a model that adjusted for age only, 0.77 (95 % CI 0.61, 0.99) in a model that controlled for parity, age at first birth, and other reproductive/hormonal factors, and 0.83 (95 % CI 0.70, 0.98) in a model that additionally controlled for other breast cancer risk factors such as alcohol consumption and use of hormone supplements. Similar associations were seen among premenopausal women and in an analysis restricted to ER+PR+ tumors.Reproductive factors explained some of the higher incidence of ER+ tumors among white women as compared to black women.

Epidemiologic studies have yet to provide consistent evidence to support a protective effect of aspirin and other non-steroidal anti-inflammatory drugs (NSAID) on the incidence of breast cancer.We evaluated the relations of current use of aspirin, non-aspirin NSAIDs, and acetaminophen with breast cancer incidence in the Black Women's Health Study.Biennial follow-up of 59,000 study participants began in 1995. During 558,600 person-years of follow-up through 2007, 1,275 breast cancer cases were identified. Using Cox proportional hazards regression, we estimated incidence rate ratios (IRR) and 95% confidence intervals (CI) for associations of current and former use of aspirin, other NSAIDs, and acetaminophen with incident breast cancer.After adjustment for age, education, body mass index at age 18, physical activity, female hormone use, current smoking, and other NSAID use, the IRRs were 0.79 (95% CI = 0.66, 0.95) for current aspirin use and 0.68 (95% CI = 0.50, 0.92) for ≥5 years of aspirin use. Similar associations were observed for acetaminophen use.Both aspirin and acetaminophen use were inversely associated with breast cancer incidence in the present study. Reasons for the association with acetaminophen use are unclear, given that acetaminophen has very weak anti-inflammatory effects.

Prospective studies of tea and coffee intake and breast cancer risk have yielded inconsistent results. None of these studies has reported separately on African-American women. We prospectively examined the relation of tea and coffee consumption to risk of breast cancer among 52,062 women aged 21–69 at enrollment in 1995 in the Black Women’s Health Study. Dietary intake was assessed in 1995 and 2001 using a validated food frequency questionnaire. Cox proportional hazards models were used to estimate incidence rate ratios (IRR) and 95% confidence intervals (CI), adjusted for breast cancer risk factors. During 12 years of follow-up through 2007, there were 1,268 incident cases of breast cancer. Intakes of tea, coffee, and caffeine were not significantly associated with the risk of breast cancer overall. The IRRs for consumption of ≥4 cups/day compared with none were 1.13 (95% CI 0.78–1.63) for tea and 1.03 (95% CI 0.77–1.39) for caffeinated coffee, and the IRR for the top quintile relative to the bottom quintile of caffeine intake was 1.04 (95% CI 0.87–1.24). Consumption of tea, coffee, and caffeine was not significantly associated with breast cancer risk according to menopausal status or hormone receptor status. Our findings suggest that intakes of tea, coffee, and caffeine are not associated with the risk of breast cancer among African-American women.

Relatively little research has been conducted on familial breast cancer in African American women.Data from the Black Women's Health Study, a prospective cohort study of African American women, were used to assess breast cancer risk in relation to family history of cancer. Since 1995, participants have completed biennial postal questionnaires on health status, risk factors, and family history of cancer. Cox proportional hazards analyses were used to calculate incidence rate ratios (IRRs) and 95% confidence intervals (CI) for family history of breast and other types of cancer.Among 57,364 participants who were cancer-free at baseline, 1,306 incident breast cancer cases occurred during 12 years of follow-up. The IRR for a first-degree family history of breast cancer relative to no family history was 1.78 (95% CI 1.55-2.06). IRRs varied by the age at diagnosis, from 1.60 (or=age 55) to 2.76 (age 35). Results were consistent across subtypes of breast tumor defined by estrogen and progesterone receptor status. Breast cancer risk was also associated with family history of colon cancer (IRR 1.35, 95% CI 1.12-1.63) and possibly with family history of leukemia (IRR 1.42, 95% CI 0.82-2.46).These findings indicate a strong familial relationship for breast cancer in African American women. The associations with family history of colon cancer and leukemia warrant further investigation.