Sarink D, White KK, Loo LWM, et al. - Oral contraceptive use (OC) use and obesity are associated with estrogen receptor positive (ER+) and ER- breast cancer risk. These associations differ by race/ethnicity, however, racial/ethnic differences in risk can not be completely explained by the established risk factors.

• There were a total of 81,511 participants (Native Hawaiian, Japanese American, Latina, African American, and White women) in the Multiethnic Cohort Study.

• Relative to White women, Native Hawaiians were at higher risk for ER+ breast cancer whereas Latinas and African Americans were at lower risk; African Americans were at higher risk for ER- disease.

• Associations between OC use and body mass index with ER+ disease risk differed by race/ethnicity; only Latinas exhibited increased risk in correlation with ever vs never OC use and Japanese Americans showed the strongest positive associations for obese vs lean BMI.

• For ER- disease risk, African Americans showed the strongest associations for OC use, particularly duration of use.