(ChemotherapyAdvisor) – Breastfeeding reduced risk for estrogen receptor (ER)-negative and progesterone receptor (PR)-negative breast cancer, a study conducted to examine the relationship between modifiable reproductive risk factors—such as breastfeeding and oral contraceptive use—and ER/PR breast cancer, a study presented during the 11th Annual AACR International Conference on Frontiers in Cancer Prevention Research has found.
This study included 4,011 women with breast cancer and 2,997 population-based controls from three sites of the Breast Cancer Family Registry, which includes women with and without breast cancer from the United States, Canada, and Australia.
Meghan Work, MPH, of Columbia University’s Mailman School of Public Health, New York, NY, and colleagues evaluated the association between reproductive and hormonal risk factors with ER and PR status and compared two case groups, hormone receptor positive (HR+) breast cancers and ER/PR-negative breast cancer, to the control group.
High parity without breastfeeding was positively associated only with ER/PR-negative tumors (OR 1.57, 95% CI 1.10–2.24, for ≥3 live births vs nulliparity). When high parity was coupled with breastfeeding, it was no longer associated with ER/PR-negative 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 use—with the exception of formulations available before 1975—was not found to be associated with ER/PR-negative cancer risk. “These earlier formulations contained higher doses of estrogen and progestin than more recent versions,” Work said, and such use was associated with an increased risk of ER/PR-negative cancer (OR 1.32; 95%CI 1.04–1.67). Oral contraceptive 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).
These results are in line with data that have shown a benefit for breastfeeding in triple-negative breast cancer. “As there are few modifiable factors for ER/PR-negative breast cancers, our findings lend further support to the potential that may be gained through greater promotion of breastfeeding to women at risk of [these] cancers,” Work concluded.