A prospective study of endometriosis and risk of benign breast disease

Among women in the Nurses’ Health Study II followed from 1991–2003 (n = 76,393), we investigated the association between laparoscopically confirmed endometriosis and biopsy-confirmed BBD. Cox proportional hazard models, adjusted for a priori potential confounding factors, were used to calculate hazard ratios (HR) and 95 % confidence intervals (CI). Across follow-up, 2011 BBD biopsies were collected and centrally reviewed by study pathologists (nonproliferative = 675, proliferative = 1336). Effect modification by infertility history and use of screening mammography was investigated.

Endometriosis was associated with a modest increased risk of biopsy-confirmed BBD in crude and multivariable adjusted models (HR 1.20, 95 % CI 1.00–1.43). When evaluating subtypes of BBD, we did not see different associations for nonproliferative or proliferative BBD lesions, as endometriosis was associated with a modest increased risk for both (HR nonproliferative 1.15, 95 % CI 0.84–1.57; HR proliferative 1.22, 95 % CI 0.98–1.52). The association between endometriosis and proliferative BBD appeared strongest among women who had ever experienced infertility (HR 1.50, 95 % CI 1.12–2.03; P value, test for heterogeneity = 0.05). Sensitivity analyses investigating screening behaviors between those with and without endometriosis did not significantly alter results.