Researchers identify breast cancer risk factors for younger, black women

Black women under the age of 45 are at increased risk for an aggressive form of breast cancer [estrogen receptor (ER) negative] if they experienced a high number of pregnancies, never breast fed, and/or had higher waist-to-hip ratio. These findings appear in Cancer Epidemiology, Biomarkers, & Prevention.

Mortality from breast cancer is markedly higher in African American women as compared to white women in the U.S., in part because they are more likely to be diagnosed with ER-negative tumors, which are more aggressive and difficult to treat. African American women are also diagnosed with breast cancer at younger ages.

Researchers from Boston University's Slone Epidemiology Center used 18 years of data from 57,708 African American women enrolled in the Black Women's Health Study, a follow-up study of the health of African American women in progress since 1995. They evaluated the relation of reproductive factors, measures of body size, and other factors to incidence of ER-negative and ER-positive breast cancer in both younger and older women.

"Very little is known about how young women can reduce their personal risk of ER-negative ," said Kimberly Bertrand, ScD, epidemiologist at the Slone Epidemiology Center at Boston University and assistant professor of medicine at Boston University School of Medicine, who led this study. "Most exciting among our findings is that two of the factors we found to be important—breastfeeding and higher waist-to-hip ratio—are modifiable, which suggests opportunities for risk reduction or prevention."

More information: K. A. Bertrand et al. Differential patterns of risk factors for early-onset breast cancer by ER status in African American women, Cancer Epidemiology Biomarkers & Prevention (2016). DOI: 10.1158/1055-9965.EPI-16-0692

Background: Given the disproportionately high incidence of early-onset breast cancer and aggressive subtypes such as estrogen receptor (ER) negative tumors in African American (AA) women, elucidation of risk factors for early-onset of specific subtypes of breast cancer is needed. Methods: We evaluated associations of reproductive, anthropometric, and other factors with incidence of invasive breast cancer by age at onset (<45, {greater than or equal to}45) in 57,708 AA women in the prospective Black Women's Health Study. From 1995 through 2013, we identified 529 invasive breast cancers among women <45 years of age (151 ER-, 219 ER+) and 1,534 among women {greater than or equal to}45 years (385 ER-, 804 ER+). We used multivariable Cox proportional hazards regression to estimate hazard ratios (HRs) for associations by age and ER status. Results: Higher parity, older age at first birth, never having breastfed, and abdominal adiposity were associated with increased risk of early-onset ER- breast cancer: HRs were 1.71 for {greater than or equal to}3 births versus one birth; 2.29 for first birth before age 25 versus <20 years; 0.61 for ever having breastfed versus never; and 1.64 for highest versus lowest tertile of waist-to-hip ratio. These factors were not associated with ER- cancer in older women or with ER+ cancer regardless of age. Conclusions: Differences in risk factors by ER subtype were observed for breast cancer diagnosed before age 45. Impact: Etiological heterogeneity by tumor subtype in early-onset breast cancer, in combination with a higher prevalence of the risk factors in AA women, may explain, in part, racial disparities in breast cancer incidence.

Citation: Researchers identify breast cancer risk factors for younger, black women (2016, October 19) retrieved 17 July 2024 from
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