Breast-feeding Reduced Risk for ER/PR-negative Breast Cancer

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Newswise — ANAHEIM, Calif. — Breast-feeding reduced the risk for estrogen receptor-negative and progesterone receptor-negative breast cancer, according to results presented at the 11th Annual AACR International Conference on Frontiers in Cancer Prevention Research, held here Oct. 16-19, 2012.

“We found an increased risk for estrogen receptor- and progesterone receptor- (ER/PR) negative breast cancer in women who do not breast-feed, but in women who have children and breast-feed, there is no increased risk,” said Meghan Work, M.P.H., doctoral student in the department of epidemiology at Columbia University’s Mailman School of Public Health in New York, N.Y.

Work and colleagues examined the relationship between reproductive risk factors — such as the number of children a woman delivers, breast-feeding and oral contraceptive use — and ER/PR-negative breast cancer. ER/PR-negative breast cancer often affects younger women and has a poor prognosis, according to Work.

The researchers used data from three sites of the Breast Cancer Family Registry, which includes women with and without breast cancer from the United States, Canada and Australia. This study included 4,011 women with breast cancer and 2,997 population-based controls.

The results indicated that having three or more children without breast-feeding was associated with an increased risk for ER/PR-negative breast cancer.

“Women who had children but did not breast-feed had about 1.5 times the risk for ER/PR-negative breast cancer when compared with a control population,” Work said. “If women breast-fed their children, there was no increased risk for ER/PR-negative cancer.”

Further, the researchers found that oral contraceptive use was not associated with ER/PR-negative cancer risk, with the exception of those formulations available before 1975. “These earlier formulations contained higher doses of estrogen and progestin than more recent versions,” Work said.

These findings are in line with previous findings that have demonstrated breast-feeding benefit in triple-negative breast cancer. “This is particularly important as breast-feeding is a modifiable factor that can be promoted and supported through health policy,” Work said.

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Abstract:B98 Parity, breastfeeding and oral contraceptive use and risk of estrogen- and progesterone-negative breast cancer in the Breast Cancer Family Registry. Meghan E. Work(1), Esther M. John(2), John L. Hopper(3), Irene L. Andrulis(4), Mary Beth Terry(1). (1)Columbia University Mailman School of Public Health, New York, NY, (2)Cancer Prevention Institute of California, Fremont, CA, (3)University of Melbourne, Melbourne, Victoria, Australia, 4Mount Sinai Hospital, Toronto, Ontario, Canada.

Introduction: Estrogen receptor (ER) and Progesterone receptor (PR) negative breast cancer (ER-PR-) is associated with poor prognosis. Little is known about modifiable risk factors, such as oral contraceptive use or breastfeeding, that can reduce risk of this cancer type; however, emerging evidence suggests that increased parity without breastfeeding may increase the risk of ER-PR- breast cancer, and that breastfeeding specifically will reduce this increased risk. Using population-based ascertained breast cancer cases from the Breast Cancer Family Registry (BCFR), we examined reproductive risk factors in relation to ER-PR- breast cancer. Methods: Using data from 4,011 incident invasive breast cancer cases and 2,997 population-based controls from the BCFR, we evaluated the association between reproductive and hormonal risk factors with ER and PR status using unordered polytomous logistic regression, comparing two case groups, hormone receptor positive (HR+) breast cancers and ER-PR- breast cancer, to the control group. Results: High parity without breastfeeding was positively associated only with ER-PR- tumors (odds ratio [OR] =1.57, 95% confidence interval [CI], 1.10-2.24, for ≥3 live births vs. nulliparity). High parity, when coupled with breastfeeding, was no longer associated with ER-PR- breast cancer (OR=0.93, 95%CI 0.71-1.22), and was inversely associated with all other HR+ cancers (OR=0.82, 95%CI 0.68-0.98). Parity (≥1 live birth vs. nulliparity), regardless of breastfeeding history, was protective against HR+ cancers only among postmenopausal women (OR=0.69, 95%CI 0.50-0.94). Oral contraceptive (OC) use was inversely associated with HR+ cancer (OR=0.82, 95%CI 0.69-0.96), but not associated with ER-PR- cancer. However, we found that OC use that commenced prior to 1975 was associated with an increased risk of ER-PR- cancer (OR=1.32, 95%CI 1.04-1.67), whereas OC use remained inversely associated with HR+ cancer only among women who began use in 1975 or later (OR=0.59, 95% CI 0.48-0.72). Conclusion: As there are few modifiable factors for ER-PR- breast cancers, our findings lend further support to the potential that may be gained through greater promotion of breastfeeding to women at risk of ER-PR- breast cancers, and indicate that OC use is not a source of increased risk for these women.