A large collaborative study provides new evidence that African-American women may be able to significantly reduce their risk of developing aggressive forms of breast cancer by breastfeeding. The study, published online ahead of print in the Journal of the National Cancer Institute, is based on a collaborative research effort led by researchers at Roswell Park Cancer Institute (RPCI), Boston University's Slone Epidemiology Center and the University of North Carolina Lineberger Cancer Center.
African-American women have a disproportionately high incidence of two aggressive forms of the disease: estrogen-receptor-negative (ER-negative) and triple-negative breast cancer, in which tumor cells test negative for three key hormone receptors. Earlier studies have shown a connection between the number of times a woman has given birth, or parity, and increased risk of ER-negative tumors, and that breastfeeding reduced risk of these aggressive breast cancers, but this large new study provides the most conclusive evidence to date of these connections.
Researchers from the three institutions formed the AMBER Consortium, or African American Breast Cancer Epidemiology and Risk Consortium, by combining four epidemiologic studies with large numbers of African-American participants: the Black Women's Health Study (BWHS), Multiethnic Cohort Study (MEC), Carolina Breast Cancer Study (CBCS) and Women's Circle of Health Study (WCHS).
Looking at questionnaire data from these studies - two cohort studies and two case-control studies of breast cancer in African-American women, they found that parous women, those who had given birth, had a 33% higher risk of ER-negative breast cancer and a 37% higher risk of triple-negative breast cancer than those who had never given birth. Breastfeeding modified the association, however; women who had breastfed had a lower risk of ER-negative and triple-negative breast cancer than women who had never breastfed. The authors of an accompanying editorial suggest that, if breastfeeding had the same prevalence in African-American women as in non-Hispanic white women, the incidence of triple-negative breast cancer in parous African-American women could be lowered by almost two-thirds.
"Our findings suggest that parous women are at increased risk of ER- and triple-negative breast cancer, and that lactation may ameliorate the effects of pregnancy and childbirth," the authors note. "This may explain, in part, why African-American women, who typically have more children but a lower prevalence of lactation than U.S. white women, are disproportionately affected by ER- breast cancer."
"These findings showing that breastfeeding can reduce the risk for African-American women of getting aggressive breast cancers are exciting because this is something that can be acted upon, where we can actually prevent some cases of these often-deadly cancers," says co-author Dr. Ambrosone, Chair of the Department of Cancer Prevention and Control at RPCI and of three co-principal investigators on the study. "We already know that breastfeeding has so many benefits to babies and their mothers. This is one more reason to encourage and support breastfeeding, particularly for African-American women."
In all, the study involved 14,180 women without cancer, 2,446 ER+ breast cancer case patients and 1,252 ER-negative breast cancer case patients, 567 of whom could be classified as triple-negative.
Dr. Ambrosone and her fellow co-PIs, Dr. Julie Palmer, ScD, from BU's Slone Center and Andrew Olshan, PhD, from the Lineberger Center at UNC, are currently researching additional hypotheses as part of the AMBER Consortium. "We're hopeful that this collaboration will lead to many new insights and discoveries that can be used to prevent aggressive breast cancer in African-American women," says Dr. Ambrosone.
The authors note that information on length of lactation, exclusivity of breastfeeding, or characterization of weaning was not available for all women in the study, and that they were therefore not able to estimate the minimum duration required for a reduction in risk of ER-negative cancer.