Oct 29, 2015 01:26 AM EDT By J Dionne, UniversityHerald Reporter

New research suggests that breastfeeding may lower a woman's risk of developing breast cancer.

An international team of researchers found 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 percent in women who breastfed.

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. In the United States, this subtype represents about 20 percent of all breast cancers.

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.

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

HRN 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.

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.

Based on the findings, researchers say 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," said Farhad Islami, director of interventions, Surveillance and Health Services Research at 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," Paolo Boffetta, associate director for population sciences at the Tisch Cancer Institute at the Icahn School of Medicine at Mount Sinai, said in a statement.

Boffetta said more research is necessary to further understand the full impact of breastfeeding duration and its effect on other subtypes.

The analysis is detailed in the journal Annals of Oncology.

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