Is there an association between long-term tamoxifen treatment and the development of carcinosarcoma (malignant mixed Müllerian tumor) of the uterus?

A cluster of five patients with endometrial carcinosarcoma (malignant mixed Müllerian tumor) occurred at our center during 1993; four of these had been prescribed long-term tamoxifen for breast carcinoma. Searching the archives for the 9-year period 1983-1992 revealed two further cases of uterine carcinosarcoma occurring in patients prescribed tamoxifen, from a total of 16 cases of this tumor. Five of the six patients diagnosed with carcinosarcoma who had been taking tamoxifen had been maintained on the drug for at least 6 years, while the other had a 3-year history of tamoxifen therapy. From these data we raise the question of an association between long-term tamoxifen treatment and development of endometrial carcinosarcoma, following the dramatic increase in the prescribing of this drug after 1984.