Breastfeeding Lowers Risk of Aggressive Type of Breast Cancer

Mother and Baby Breast Feeding Drawing

AICR research currently shows there is strong evidence that mothers who breastfeed are at lower risk of developing breast cancer. Now comes a large study that adds to the research, finding that breastfeeding links to a lower risk of developing an aggressive form of breast cancer called hormone-receptor negative. The study was published in Annals of Oncology.

Tumors that are hormone-receptor negative do not have receptors for hormones and thus, do not respond to hormonal treatments such as tamoxifen or aromtase inhibitors. These cancers are often more deadly because of the treatment challenges and the fact that they are not diagnosed until later stages.

This new study analyzed the research on the links between breastfeeding and breast tumors by receptor: estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 (HER2) status. Researchers analyzed 27 studies (8 cohort and 19 case–control) that included almost 37,000 breast cancer cases.

After adjusting for age, obesity, family history and other risk factors, the study found that breastfeeding at any time was associated with a 10 percent lower risk of breast tumors that were negative for both estrogen and progesterone receptors when compared to women who never breastfed. This protective effect was even stronger for triple negative tumors -- those negative for estrogen, progesterone and HER2 receptors -- but this was based on a smaller number of studies.

This analysis showed no protective link between breastfeeding and the risk of the more common breast tumors, those positive for estrogen and progesterone. Some of the studies included did find a protective effect, the authors note; more research is needed.

How breastfeeding may protect agains breast tumors in under study, possible mechanism include its effect on hormones and changes to immune responses.

No funding or support was noted.

Source:  F. Islami, Y. Liu, A. Jemal, J. Zhou, E. Weiderpass, G. Colditz, P. Boffetta, M. Weiss. Breastfeeding and breast cancer risk by receptor status—a systematic review and meta-analysis. Annals of Oncology, 2015; mdv379iam Bourke et al.

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    Published on January 31, 2016

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