WASHINGTON — Results from the Black Women's Health Study show two or more full-term births are linked to a higher incidence of certain breast cancers in Black women, but only in those who did not breast-feed
The study is being reported online in Cancer Epidemiology, Biomarkers & Prevention.
"African-American women are more likely to have had a greater number of full-term births and less likely to have breastfed their babies," said lead author Julie R. Palmer, ScD, professor of epidemiology at the Slone Epidemiology Center at Boston University in Boston, Massachusetts, in a news release. "This study shows a clear link between that and hormone receptor-negative breast cancer."
The study cohort consisted of 59,000 African American women observed with biennial questionnaires. Review of pathology data confirmed 457 incident cases of ER+/PR+ and 318 cases of ER−/PR− breast cancer from 1995 through 2009. Proportional hazards regression models controlling for age, reproductive characteristics, and risk factors for breast cancer allowed determination of hazard ratios (HRs) and 2-sided 95% confidence intervals (CIs) for the incidence of breast cancer subtypes.
The risk for ER−/PR− breast cancer was increased with higher parity (HR, 1.48; 95% CI, 0.98 - 1.84 for 3+ vs 0 births; P = .009 for trend), whereas the risk for ER+/PR+ cancer was decreased (HR, 0.53; 95% CI, 0.39 - 0.73 for 3+ vs 0 births; P = .0002 for trend). High parity was not associated with an increased incidence of ER−/PR− breast cancer among women who had breast-fed, but the inverse association with ER+/PR+ cancer was still present.
"The adverse effect of high childbirth without subsequent breast-feeding seems to be confined to the hormone receptor–negative breast cancer, which carries a higher mortality rate and is more common in African-Americans," Dr. Palmer said.
Limitations of this study include possible selection bias, inability to assess subtypes according to HER2 expression, and limited ability to evaluate associations by duration of breast-feeding because most participants who had breast-fed had done so for a total of less than 12 months.
"The higher incidence of ER−/PR− breast cancer in African American women may be explained in part by their higher parity and lower prevalence of breastfeeding relative to white women," the study authors conclude. "Increased breastfeeding may lead to a reduction in the incidence of this breast cancer subtype."