Background: Convincing epidemiologic evidence links excess body mass to increased risks of endometrial and postmenopausal breast cancers, but the relation between body mass index (BMI) and ovarian cancer risk remains inconclusive. Potential similarities regarding a hormonal mechanism in the etiology of female cancers highlight the importance of investigating associations according to menopausal hormone therapy (MHT) use. However, to the authors' knowledge, data addressing whether the relation between BMI and ovarian cancer differs by MHT use are very sparse.
Methods: The authors prospectively investigated the association between BMI and ovarian cancer among 94,525 US women who were followed between 1996 through 1997 to December 31, 2003. During 7 years of follow-up, 303 epithelial ovarian cancer cases were documented.
Results: Compared with normal weight women (BMI of 18.5-24.9 kg/m(2)), the multivariate relative risk (MVRR) of ovarian cancer for obese women (BMI of >or=30 kg/m(2)) in the cohort as a whole was 1.26 (95% confidence interval [95% CI], 0.94-1.68). Among women who never used MHT, the MVRR for obese versus normal weight women was 1.83 (95% CI, 1.18-2.84). In contrast, no relation between BMI and ovarian cancer was apparent among women who ever used MHT (MVRR = 0.96; 95% CI, 0.65-1.43; P interaction = 0.02). Exploratory analyses also suggested a positive association between BMI and ovarian cancer among women without a family history of ovarian cancer (MVRR comparing obese vs normal weight women = 1.36; 95% CI, 1.00-1.86), but no relation with BMI was apparent among women with a positive family history of ovarian cancer (MVRR = 0.74; 95% CI, 0.34-1.62 [P interaction = .02]).
Conclusions: Based on the results of the current study, the authors suspect that obesity is associated with enhanced ovarian cancer risk through a hormonal mechanism.