Uterine malignant mixed müllerian tumor in a patient on long-term tamoxifen therapy for breast cancer.

A case of malignant mixed müllerian tumor of the uterus, heterologous type, in an 83-year-old woman on tamoxifen (TAM) therapy for 9 years for breast cancer is presented. Benign endometrial polyps were diagnosed on endometrial curettings for postmenopausal bleeding after the patient had been on TAM for 5 years. Recurrent postmenopausal bleeding developed 4 years later. Endometrial curettings and hysterectomy revealed a 10-cm polypoid malignant mixed müllerian tumor (MMMT) and endometrial polyps. There was no invasion of the myometrium or endocervix and no evidence of metastatic tumor in 13 pelvic lymph nodes, peritoneal washings, or omentum. TAM has been associated with the development of endometrial polyps, hyperplasia, and adenocarcinoma possibly mediated through its agonistic estrogenic properties. Only one other case of MMMT arising in patients on TAM therapy has been previously reported, but may also be a consequence of the estrogenic effects of TAM therapy.