Effect of raloxifene on endometrial cancer risk in a population-based, case-control study

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5001 Background: Raloxifene, a selective estrogen receptor modulator, has been shown to reduce breast cancer risk in women with osteoporosis, and is currently being compared to tamoxifen for breast cancer chemoprevention in the “STAR” trial. In contrast to tamoxifen, raloxifene does not stimulate endometrial estrogen receptors, and may therefore be associated with a lower risk of endometrial cancer compared with tamoxifen. However, there are few data available on the absolute risk of endometrial cancer in users of raloxifene, or the relative risks of endometrial cancer among raloxifene and tamoxifen users in the general population. Methods: We performed a population-based, case-control study of breast and endometrial cancer. Cases had pathologically-confirmed endometrial cancer, and resided in a 9-county area surrounding Philadelphia. Controls with no history of endometrial cancer were obtained through random-digit dialing and matched to cases by age and race. Only African-American and Caucasian women were included in the study. Results: A total of 547 cases and 1412 controls were included in the current analysis. Among cases, 18 (3.3%) ever used raloxifene and 34 (6.2%) ever used tamoxifen. Among controls, 93 (6.6%) ever used raloxifene and 34 (2.2%) ever used tamoxifen. Compared to non-users, the odds ratio for development of endometrial cancer was 0.43 (95% CI 0.26 - 0.73) for raloxifene users, and 2.35 (95% CI 1.43 - 3.86) for tamoxifen users. After adjustment for other confounders, including BMI and previous history of breast cancer, the odds ratio associated with developing endometrial cancer among raloxifene users was 0.50 (95% CI 0.29 - 0.85), while the odds ratio among tamoxifen users was 1.50 (95% CI 0.77 - 2.92). The benefit of raloxifene on endometrial cancer risk remained even among those with short-term use (<3 years). Conclusions: Raloxifene use was associated with a 50% reduction in the odds of developing endometrial cancer in this population-based case-control study. These data suggest a possible protective effect of raloxifene on the endometrium, providing a further benefit to this drug in cancer chemoprevention. No significant financial relationships to disclose.

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