Women who breastfeed may have up to 20 per cent reduced risk of developing an aggressive form of breast cancer, a large international study has found.
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, the researchers said.
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.
A large international study, published in Annals of Oncology, has found that breastfeeding is associated with a lower risk of developing HRN breast cancer.
The evidence showed that the risk was reduced by up to 20 per cent in women who breastfed, researchers said.
In the US, HRN breast cancers represent about 20 per cent 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 often deadly because they tend to be diagnosed at later stages, respond to fewer treatment options, and are less likely to be cured.
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," said Marisa Weiss, president and founder of Breastcancer.Org, and director of breast health outreach at Lankenau Medical Centre in US.
"Breastfeeding is a relatively accessible, low-cost, short-term strategy that yields long-lasting natural protection," said Weiss.
"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," said Paolo Boffetta, associate director for population sciences at the Tisch Cancer Institute at the Icahn School of Medicine at Mount Sinai in US.
