Racial differences in the association of body mass index and ovarian cancer risk in the OCWAA Consortium

Background: Obesity disproportionately affects African American (AA) women and has been shown to increase ovarian cancer risk, with some suggestions that the association may differ by race. Methods: We evaluated body mass index (BMI) and invasive epithelial ovarian cancer (EOC) risk in a pooled study of case–control and nested case–control studies including AA and White women. We evaluated both young adult and recent BMI (within the last 5 years). Associations were estimated using multi-level and multinomial logistic regression models. Results: The sample included 1078 AA cases, 2582 AA controls, 3240 White cases and 9851 White controls. We observed a higher risk for the non-high-grade serous (NHGS) histotypes for AA women with obesity (OR_{BMI 30+}= 1.62, 95% CI: 1.16, 2.26) and White women with obesity (OR_{BMI 30+}= 1.20, 95% CI: 1.02, 2.42) compared to non-obese. Obesity was associated with higher NHGS risk in White women who never used HT (OR_{BMI 30+}= 1.40, 95% CI: 1.08, 1.82). Higher NHGS ovarian cancer risk was observed for AA women who ever used HT (OR_{BMI 30+}= 2.66, 95% CI: 1.15, 6.13), while in White women, there was an inverse association between recent BMI and risk of EOC and HGS in ever-HT users (EOC OR_{BMI 30+}= 0.81, 95% CI: 0.69, 0.95, HGS OR_{BMI 30+}= 0.73, 95% CI: 0.61, 0.88). Conclusion: Obesity contributes to NHGS EOC risk in AA and White women, but risk across racial groups studied differs by HT use and histotype.