Body size and the risk of endometrial cancer by hormone therapy use in postmenopausal women in the California Teachers Study cohort

Objective To investigate whether hormone therapy (HT) and obesity are associated with endometrial cancer risk among postmenopausal women in the California Teachers Study cohort. Methods Of 28,418 postmenopausal women, 395 developed type 1 endometrial cancer between 1995 and 2006. Multivariate Cox regression was performed to estimate relative risks (RR), stratified by HT use (never used, ever estrogen alone (ET) or exclusively estrogen-plus-progestin (EPT)). Results Among women who never used HT, overall and abdominal adiposity were associated with increased risk; when evaluated simultaneously, abdominal adiposity was more strongly associated (RR 2.2, 95% confidence interval (CI): 1.1-4.5 for waist >= 35 vs. <35 inches). Among women who ever used ET, risk was increased in women with BMI >= 25 kg/m(2) (RR 1.6, 95% CI: 1.1-2.3 vs. <25 kg/m(2)). Neither overall nor abdominal obesity was associated with risk in women who exclusively used EPT (p-interaction <0.001 for BMI by HT use). Conclusions Among women who never used HT, risk was strongly positively related to obesity and may have been influenced more by abdominal than by overall adiposity; however, due to small numbers, this latter finding requires replication. Among women who ever used ET, being overweight at baseline predicted higher risk, whereas use of EPT mitigated any effects of obesity.