This post has been corrected. See note at the bottom for details.
African American women have higher rates of a type of breast cancer that isn't dependent for growth on the hormones estrogen or progesterone. They also have a higher rate of childbearing than do white American women.
A new study finds there is likely a link between those two facts -- that bearing a baby to term raises the risk for this type of cancer, called estrogen or progesterone receptor-negative breast cancer.
The study also finds that black women who breastfeed their babies can lower their odds of developing this cancer back down again.
The study, published Tuesday in the journal Cancer Epidemiology, Biomarkers & Prevention, followed a group of 47,000 African American women from 1996 through 2009. Researchers had participants fill out, every two years, a detailed questionnaire assessing a wide range of factors that affect a woman's risk for breast cancer -- including weight, age at which they began menstruating, pregnancies and age of first childbearing, birth control or hormone-replacement use, physical activity and alcohol consumption.
What they found was that African American women who had given birth to more children were more likely to develop estrogen or progesterone-negative cancer than their peers who had not given birth or who had given birth to only one child. But when a woman with two or more childbirths breastfed her babies, that risk declined considerably.
The authors -- epidemiologists from Boston University, Georgetown University and Roswell Park Cancer Institute in Buffalo, N.Y. -- surmised that given the prevalence of infectious diseases in Africa, women of African origins may respond to pregnancy with a particularly strong immune response, which in turn can allow cancers to gain a foothold in the body. Lactation, they noted, appears to blunt that effect.
Estrogen or progesterone receptor-negative breast cancers are less common than those that are fueled by those hormones, representing just one in four breast cancers. But they tend to be more aggressive and harder to treat.
Despite aggressive public health campaigns touting the benefits -- to mother and child -- of breastfeeding, the practice is less common among African American women than among white women. Future efforts to promote breastfeeding, wrote the authors, should let African American women know that moms who nurse their babies may also reduce their odds of developing a breast cancer that affects them disproportionately and is difficult to treat.
[For the Record, 12:25 p.m. Aug. 19: An earlier version of this post said Roswell Park Cancer Institute is in Rochester, N.Y.]