Boston University Identifies Contributors To High Breast Cancer Incidence In African-American Women

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.


Their study, based on the ongoing Black Women's Health Study, which has followed 59,000 African American women since 1995, found that giving birth to two or more children was associated with a 50 percent increase in the incidence of estrogen and progesterone receptor negative (ER-/PR-) cancers, but only among women who had not breastfed.


ER- and PR-negative results mean that the growth of the cancer is not supported by the hormones estrogen and progesterone, and therefore does not respond to hormonal therapy (such as tamoxifen or aromatase inhibitors). It's the type of cancer "Good Morning America" anchor Robin Roberts was diagnosed with back in 2007 and accounts for 10 to 20 percent of breast cancers -- more than one out of every 10 -- according to Breastcancer.org.


Over the study's 14 year follow-up, 318 women developed ER-/PR- breast cancers, while 457 developed breast cancers with estrogen and progesterone receptors (ER and PR positive).


What was also striking, was that having two or more children was associated with a decreased risk for ER and PR positive breast cancer, a form that is more common among white women. Breast feeding had no influence on that association.


"Our results, taken together with recent results from studies of triple negative and basal-like breast cancer, suggest that breastfeeding can reduce risk of developing aggressive, difficult-to-treat breast cancers," explained lead author Julie Palmer, ScD, MPH, a senior epidemiologist at the Slone Epidemiology Center and a professor of epidemiology at Boston University School of Public Health,.