Breastfeeding could reduce risk of aggressive form of breast cancer that disproportionately affects black, younger women

Aug 26 2008

Breastfeeding for at least six months might lower the risk of developing so-called "triple negative" breast cancer, an aggressive form of the disease that is more common in black and younger women, according to a study published on Monday in the journal Cancer, the Seattle Post-Intelligencer reports (Paulson, Seattle Post-Intelligencer, 8/24).

Nearly 50% of black women younger than age 55 who are diagnosed with breast cancer have the triple negative type, compared with 22% of white women. The five-year survival rate for triple negative breast cancer is 15% lower than for other types of the disease, in part because the disease responds poorly to most breast cancer treatments (Kaiser Health Disparities Report, 5/30).

To determine what puts women at risk for the triple negative type of breast cancer, lead researcher Amanda Phipps, a scientist in the public health division of the Fred Hutchinson Cancer Research Center, and colleagues studied two groups of women ages 55 to 79. One group was made up of 1,140 women who had several different forms of breast cancer, including the triple negative type, the most common "luminal" form and another form associated with the HER2 protein. The second group was made up of 1,476 women who had not been diagnosed with breast cancer.

Researchers took into account the participants' reproductive health histories, which would provide indicators of hormone levels over time, such as breastfeeding practices and the onset of menstruation and menopause.

Among other findings, researchers found that breastfeeding for at least six months corresponded with a lower risk of developing the triple-negative form of breast cancer and the common luminal form. It is not exactly clear why breastfeeding influenced hormonal cancer risks. Phipps said, "One possible explanation is that while women are breastfeeding, they aren't menstruating and so their hormones aren't cycling," so the longer women breastfeed, the less chance their hormones have to develop a cancer. Another theory is that breastfeeding alters the structure of breast cells in a way that makes them less prone to develop into cancer cells, Phipps said.

She said the findings indicate that reproductive behavior "helps explain why some women are at higher risk and also why certain therapies are not effective against these more aggressive forms of breast cancer" (Seattle Post-Intelligencer, 8/24).

An abstract of the study is available online.