International journal of cancer | 2021
Racial/ethnic differences in postmenopausal breast cancer risk by hormone receptor status: the Multiethnic Cohort Study.
Abstract
There are racial/ethnic differences in the incidence of hormone receptor positive and negative breast cancer. To understand why these differences exist, we investigated associations between hormone-related factors and breast cancer risk by race/ethnicity in the Multiethnic Cohort (MEC) Study. Among 81,511 MEC participants (Native Hawaiian, Japanese American, Latina, African American, and White women), 3,806 estrogen receptor positive (ER+) and 828 ER- incident invasive breast cancers were diagnosed during a median of 21\u2009years of follow-up. We used Cox proportional hazards regression models to calculate associations between race/ethnicity and breast cancer risk, and associations between hormone-related factors and breast cancer risk by race/ethnicity. Relative to White women, ER+ breast cancer risk was higher in Native Hawaiians and lower in Latinas and African Americans; ER- disease risk was higher in African Americans. We observed interaction with race/ethnicity in associations between oral contraceptive use (OC; pint 0.03) and body mass index (BMI; pint 0.05) with ER+ disease risk; ever vs never OC use increased risk only in Latinas and positive associations for obese versus lean BMI were strongest in Japanese Americans. For ER- disease risk, associations for OC use, particularly duration of use, were strongest for African Americans (pint 0.04). Our study shows that associations of OC use and obesity with ER+ and ER- breast cancer risk differ by race/ethnicity, but established risk factors do not fully explain racial/ethnic differences in risk. Further studies are needed to identify factors to explain observed racial/ethnic differences in breast cancer incidence. This article is protected by copyright. All rights reserved.