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Study shows association between breastfeeding and reduced risk of aggressive breast cancer

New meta-analysis shows lower incidence of hormone receptor negative breast cancer in women who breastfed

American Cancer Society

A large international study shows that breastfeeding is associated with a lower risk of developing an aggressive form of breast cancer called hormone-receptor negative. This new combined evidence shows the risk was reduced by up to 20% in women who breastfed. Published in Annals of Oncology, this breastfeeding meta-analysis is a collaboration between; Icahn School of Medicine at Mount Sinai; Washington University, St. Louis; and the American Cancer Society.

Hormone-receptor-negative (HRN) breast cancers are more likely to be aggressive and life-threatening. This subtype is more commonly diagnosed in women under age 50. Women of African American or Sub-Saharan African descent are more likely to be diagnosed with HRN breast cancers, as are women with the BRCA1 gene mutation. Other factors may put these women at even higher risk for developing HRN breast cancer, including obesity and multiple early pregnancies. Furthermore, women with these multiple risk factors are least likely to breastfeed.

In the United States, HRN breast cancers represent about 20% of all breast cancers. This subtype of breast cancer has no receptors for the hormones estrogen or progesterone; about two-thirds of these HRN cancers also have no receptors for HER2 (human epidermal growth factor receptor 2). Breast cancers with no receptors for estrogen, progesterone, or HER2 are called triple negative (TN).

HRN and TN breast cancer are more often deadly because they tend to be diagnosed at later stages, respond to fewer treatment options, and are less likely to be cured by current therapies. In the absence of the receptors for estrogen, progesterone, and HER2, medicines that target these receptors--such as tamoxifen, aromatase inhibitors, Herceptin, and Perjeta--are ineffective and thus have no role in treating these patients.

"Further evidence to support the long-term protection of breastfeeding against the most aggressive subtypes of breast cancer is very encouraging and actionable," says Marisa Weiss, M.D., president and founder,, and director of breast health outreach, Lankenau Medical Center. "Breastfeeding is a relatively accessible, low-cost, short-term strategy that yields long-lasting natural protection."

This work highlights the need for more public health strategies that directly inform women and girls about the maternal (and fetal) benefits of breastfeeding before and during a woman's child-bearing years. It's also important for these women to have the message reinforced by their healthcare professionals.

It's critical to remove the barriers to breastfeeding at home, in the community and in the workplace. "All approaches will be necessary in order to protect the most women against the devastation of breast cancer over their lifetimes," says Farhad Islami, M.D., Ph.D., director of interventions, Surveillance and Health Services Research, American Cancer Society.

"Pregnant women and young mothers are highly receptive and motivated to make healthy choices. We need to encourage women who are able to breastfeed to do so for their breast health, in addition to the health of their children," says Paolo Boffetta, M.D., associate director for population sciences at the Tisch Cancer Institute at the Icahn School of Medicine at Mount Sinai. "Further prospective research will be necessary to further understand the full impact of breastfeeding duration and its effect on other subtypes."


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