Body size over the life-course and the risk of endometrial cancer: the California Teachers Study.

PURPOSE: Obesity is a public health epidemic and a major risk factor for endometrial cancer. Here, we identify key aspects of body size which jointly, over the life-course (since adolescence), are associated with endometrial cancer risk. METHODS: Among 88,142 participants in the California Teachers Study, 887 were diagnosed with invasive type 1 endometrial cancer between 1997-1998 and 2012. Multivariable Cox proportional hazards models provided estimates of hazard rate ratios (HR) and 95% confidence intervals (CI) for endometrial cancer associated with life-course body size phenotypes, which incorporated validated measures. RESULTS: Among women currently using hormone therapy, endometrial cancer risk was only associated with height (HR 1.78, 95% CI 1.32-2.40 for ≥67 vs. <67 inches). Among women not using hormone therapy, tall women who were overweight/obese in adolescence (HR 4.33, 95% CI 2.51-7.46) or who became overweight/obese as adults (HR 4.74, 95% CI 2.70-8.32) were at greatest risk. CONCLUSIONS: Considering absolute body mass, changes in adiposity over time, and body fat distribution together, instead of each measure alone, we identified lifetime obesity phenotypes associated with endometrial cancer risk. These results more clearly define specific risk groups, and may explain inconsistent findings across studies, improve risk prediction models, and aid in developing targeted interventions for endometrial cancer.