IV.3 The combined effects of ERT, obesity and tamoxifen therapy for breast cancer on endometrial cancer risk

Abstract

TAMOXIFEN, WIDELY used to treat breast cancer, is currently under evaluation as a breast cancer prevention agent in clinical trials. Reports that tamoxifen induces endometrial cancer have raised concern among consumers and practitioners. No prior studies of tamoxifen’s effects on endometrial cancer risk have examined the modifying effects of oestrogen replacement therapy (ERT) and obesity. We examined these effects in a matched case-control study of subsequent endometrial cancer following breast cancer conducted within four Surveillance Epidemiology and End Results (SEER) registries (Los Angeles, Iowa, Seattle, and Atlanta cases). The medical histories of 324 case-patients and 671 control-patients were established through the review of medical records and by interview. Tamoxifen use, ERT use and obesity were each statistically significant predictors of endometrial cancer risk. The effect of tamoxifen on endometrial cancer risk was duration related (trend P= 0.001); relative to non-users, women with more than 5 years exposure to tamoxifen had