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A study published in the journal Cancer Epidemiology, Biomarkers & Prevention found that giving birth to two or more children was associated with a 50 percent increase in the incidence of negative for estrogen and progesterone receptors breast cancer, but the association was not present among women who breastfed.
Giving birth to two or more children is linked to estrogen and progesterone receptor negative cancers in women who didn't breastfeed, U.S. researchers say.
Lead author Julie Palmer, a senior epidemiologist at the Slone Epidemiology Center and a professor of epidemiology at Boston University School of Public Health, said the findings are based on the ongoing Black Women's Health Study, which tracked 59,000 African-American women since 1995.
In 14 years of follow-up, 318 women developed breast cancers negative for estrogen and progesterone receptors, while 457 developed breast cancers with positive estrogen and progesterone receptors, Palmer said.
The study, published in the journal Cancer Epidemiology, Biomarkers & Prevention, found giving birth to two or more children was associated with a 50 percent increase in the incidence of negative for estrogen and progesterone receptors breast cancer, but the association was not present among women who breastfed.
Background: Estrogen receptor (ER)-negative breast tumors and progesterone receptor (PR)-negative breast tumors occur more commonly in women of African ancestry. Recent research indicates that the effects of reproductive factors may differ by hormone receptor status. We assessed the relation of parity and lactation to incidence of ER−/PR− and ER+/PR+ breast cancer in a cohort of African American women.
Methods: From 1995–2009, 457 incident cases of ER+/PR+ and 318 cases of ER−/PR−breast cancer were confirmed by review of pathology data among 59,000 African American women followed in the Black Women's Health Study through biennial questionnaires. HRs and two-sided 95% CIs for the incidence of breast cancer subtypes were derived from proportional hazards regression models that controlled for age, reproductive variables, and breast cancer risk factors.
Results: Higher parity was associated with an increased risk of ER−/PR− breast cancer (HR = 1.48, 95% CI: 0.98–1.84 for 3+ versus 0 births, Ptrend = 0.009), and with a reduced risk of ER+/PR+ cancer (HR = 0.53, 95% CI: 0.39–0.73 for 3+ versus 0 births, Ptrend = 0.0002). Among women who had breastfed, high parity was no longer associated with increased incidence of ER−/PR− breast, but the inverse association with ER+/PR+ cancer persisted.
Conclusions: 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.