Ever breastfeeding may provide a protective effect against hormone receptor (HR)-negative breast cancers, a meta-analysis published online ahead of print in the journal Annals of Oncology has shown.1

Although breastfeeding has been inversely associated with overall risk of breast cancer, this association may differ between breast cancer receptor statuses.

Therefore, a team of researchers led by Marisa Weiss, MD, president and founder of Breastcancer.org, sought to conduct a systematic review and meta-analysis of case-control and prospective cohort studies to evaluate the association between breastfeeding and breast cancer by estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status.

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Researchers analyzed 27 studies that included a total of 36,881 breast cancer cases. Results showed that ever breastfeeding was associated with a 10% reduction in the risk for developing ER-negative and PR-negative breast cancer when results were adjusted for various confounding factors.

Although based on a small number of studies, researchers found that breastfeeding was associated with an approximately 20% reduction in the risk for triple-negative breast cancer.

The meta-analysis demonstrated no significant association between ever breastfeeding and the risk of ER-positive and/or PR-positive breast cancer in cohort studies; however, several case-control studies showed an inverse relationship between breastfeeding duration and the risk for ER-positive and/or PR-positive breast cancers.

“The association between breastfeeding and receptor-positive breast cancers needs more investigation,” the authors conclude.


1. Islami F, Liu Y, Jemal A, et al. Breastfeeding and breast cancer risk by receptor status—a systematic review and meta-analysis [published online ahead of print October 26, 2015]. Ann Oncol. doi:10.1093/annonc/mdv379.