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Fewer births, breastfeeding reduced risk for ER/PR-negative breast cancer among black women
Palmer JR. Cancer Epidemiol Biomarkers Prev. 2011;20(9):1-9.
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The higher incidence of hormone receptor-negative breast cancer that has been reported in black women may partially be explained by their higher parity rate and lower rate of breastfeeding compared with white women, according to a recent analysis of data from the Black Women’s Health Study.
Researchers assessed parity and breastfeeding among 318 women with estrogen receptor-negative/progesterone receptor-negative breast cancer and 457 women with estrogen receptor-positive/progesterone receptor-positive breast cancer. These cases were confirmed during 1995 to 2009 through biennial questionnaires among 59,000 women who were followed in the Black Women’s Health Study.
Controlling for age, reproductive variables and breast cancer risk factors, the researchers found that higher parity (three or more births) was associated with an increased risk for ER-negative/PR-negative breast cancer (HR=1.48) and a decreased risk for ER-positive/PR-positive breast cancer (HR=0.53).
When they evaluated only those women who breastfed, the researchers found that high parity was no longer associated with the increased risk for hormone receptor-negative breast cancer, but the decreased risk related to hormone receptor-positive breast cancer remained. For women who had never breastfed, having had two or more births increased risk for ER-negative/PR-negative breast cancer by 50% (HR=1.53), but researchers did not find much of an increase in risk associated with having had two or more births among women who had breastfed (HR=1.16).
Among women with a family history of breast cancer, ever-lactation was associated with a significantly reduced risk for ER-negative/PR-negative breast cancer (HR=0.33), although the researchers did not find this trend among women without a family history of breast cancer.
“Because African American women have had more births on average than U.S. white women, this association may explain in part why incidence of ER-negative/PR-negative breast cancer is higher in African American than white women,” the researchers wrote. “Further, the results provide evidence of a protective effect of lactation on ER-negative/PR-negative cancer, at least among women who have a family history of breast cancer.”
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