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Parity, Breastfeeding Tied to ER⁻/PR⁻ Breast Cancer Risk

WEDNESDAY, Aug. 17 (HealthDay News) -- Higher parity is associated with an increased risk of estrogen receptor (ER)-negative/progesterone receptor (PR)-negative (ER⁻/PR⁻) breast cancer in African-American women, but breastfeeding ameliorates this adverse effect, according to a study published online Aug. 16 in Cancer Epidemiology, Biomarkers & Prevention.

Julie R. Palmer, Sc.D., from Slone Epidemiology Center at Boston University, and colleagues examined the association between parity and lactation to incidence of ER⁻/PR⁻ and ER⁺/PR⁺ breast cancer in 59,000 African-American women. Data were collected from women followed in the Black Women's Health Study between 1995 and 2009, and 457 incident cases of ER⁺/PR⁺ and 318 cases of ER⁻/PR⁻ breast cancer, confirmed by review of pathology data, were identified.

The investigators found that higher parity was correlated with an increased risk of ER⁻/PR⁻ breast cancer (hazard ratio [HR], 1.48; 95 percent confidence interval [CI], 0.98 to 1.84 for three or more versus zero births), and with a lowered risk of ER⁺/PR⁺ cancer (HR, 0.53; 95 percent CI, 0.39 to 0.73 for three or more versus zero births). High parity was not correlated with an increased incidence of ER⁻/PR⁻ breast cancer among women who had breastfed. However, the inverse correlation between high parity and ER⁺/PR⁺ cancer remained.

"The higher incidence of ER⁻/PR⁻ breast cancer in African-American women may be explained in part by their higher parity and lower prevalence of breastfeeding relative to white women," the authors write. "Increased breastfeeding may lead to a reduction in the incidence of this breast cancer subtype."

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