OBJECTIVE: To examine the risk for endometrial cancer among overweight women using the World Health Organization's clinical definitions of obesity based on body mass index (BMI).
METHODS: Conducted in the early 1980s, the Cancer and Steroid Hormone study was a multicenter, population-based, case–control study of breast, ovarian, and endometrial cancers among women aged 20–54 years. Participants for the case group (n=421) were identified through cancer registries and had histologically confirmed endometrial cancer. Participants for the control group (n=3,159) were chosen by random-digit dialing methods in the same regions as those in the case group. Those in the case and control groups responded to the same questions during in-person interviews. Unconditional logistic regression was used to estimate adjusted odds ratios (ORs) and 95% confidence intervals (CIs).
RESULTS: The relationship between endometrial cancer and BMI (calculated as weight [kg]/[height (m)]2) was modified by age at last menstrual period (LMP). Of women who were younger than 45 years at LMP, those with BMIs of at least 35.0 had a greater risk of endometrial cancer (56%, 30/54) than did those with normal BMIs (4%, 59/1,492, adjusted OR 21.7, 95% CI 11.3–41.7). Of women age 45 or older at LMP, those with BMIs of at least 35.0 also had a greater risk (40%, 24/60) than did those with normal BMIs (14%, 168/1,235, adjusted OR 3.7, 95% CI 2.0–6.6). Women younger than 45 years at LMP and those with BMIs of at least 25.0 at 18 years and as adults (25%, 31/123) had an approximately sixfold increased risk (adjusted OR 5.8, 95% CI 3.4–9.8) compared with those with normal BMIs at 18 and as adults (4%, 58/1,460).
CONCLUSION: Very obese women aged 20–54 years have an elevated endometrial cancer risk, which appears heightened by early menopause.
LEVEL OF EVIDENCE: II