Breastfeeding Linked to Lower Rates of Some Breast Cancers

A new study in the journal Cancer (advance online edition) shows that particular types of breast cancer are rarer in women who breastfeed their babies for at least 6 months.

The researchers obtained data from two breast cancer studies that included approximately 2,500 women aged 55-79 in Washington state. Of this pool, 1,140 women had had breast cancer. All completed questionnaires that had questions about their history of breastfeeding, age at first menstrual period, live births, and menopause. The researchers then looked for patterns that stood out among women with any of the following types of breast cancer:

• Estrogen-sensitive breast cancer (the majority of cases)
• HER2-positive breast cancer (breast cancers with high levels of the HER2 protein)
• "Triple negative" breast cancer (breast cancers not sensitive to estrogen or progesterone and not HER2-positive)

Breastfeeding for at least six months seemed to be most protective for "triple negative" breast cancer and estrogen-sensitive breast cancer was 20% less common. The research team is not sure why this is and no one can conclude that breastfeeding prevents breast cancer or that not breastfeeding raises breast cancer risk. At the same time, observational research has linked breastfeeding to lower rates of breast cancer and more studies need to be done to formulate a true conclusion.