Risk of Malignant Mixed Mullerian Tumors After Tamoxifen Therapy for Breast Cancer Rochelle E. Curtis, D. Michal Freedman, Mark E. Sherman, Joseph F. Fraumeni, Jr. Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, MD. Correspondence to: Rochelle E. Curtis, MA, Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, DHHS, Executive Plaza South, Rm. 7042, Bethesda, MD 20892-7362 (e-mail: rcurtis@mail.nih.gov) Recent studies have indicated that the tamoxifen-related risk of uterine corpus cancer may be especially high for some uncommon cell types, although the magnitude of risk has not been quantified. We evaluated data from 39 451 breast cancer patients diagnosed from 1980 through 2000 who were initially treated with tamoxifen and found that the overall risk of subsequent uterine corpus cancer was increased more than twofold (observed-to-expected ratio [O/E] = 2.17, 95% confidence interval [CI] = 1.95 to 2.41) relative to the general SEER population. The relative risk was substantially higher for malignant mixed mullerian tumors (MMMTs) (O/E = 4.62, O = 34, 95% CI = 3.20 to 6.46) than for endometrial adenocarcinomas (O/E = 2.07, O = 306, 95% CI = 1.85 to 2.32), although the excess absolute risk was smaller—an additional 1.4 versus 8.4 cancers per 10 000 women per year, respectively. Among those who survived for 5 years or longer, there was an eightfold relative risk for MMMTs and a 2.3-fold risk for endometrial adenocarcinomas, with patients developing MMMTs having a worse prognosis. These findings indicate that tamoxifen may have delayed effects, such as the increased risk of MMMTs, rare but aggressive tumors of unclear pathogenesis. Journal of the National Cancer Institute, Vol. 96, No. 1, 70-74, January 7, 2004 Remember we are NOT Doctors and have NO medical training. This site is like an Encylopedia - there are many pages, many links on many topics. Support our work with any size DONATION - see left side of any page - for how to donate. You can help raise awareness of CAM.