Tamoxifen (Nolvadex®, AstraZeneca), a nonsteroidal antiestrogen, is used for the treatment of breast cancer.

AstraZenca has amended the local package insert for Nolvadex® (tamoxifen) to include additional information on the increased rare risk of uterine sarcoma (mostly malignant mixed Mullerian tumours) as well as the previously noted increased risk of endometrial adenocarcinoma.

Uterine sarcoma is rare, and is estimated to occur at 0.17 per 1000 women-years versus 0.01 to 0.02 for placebo. In Singapore there are 270 cases of uterine sarcoma over the period 1968 - 1997. Of these, 50 were malignant mixed Mullerian tumours.

Since 1978, when tamoxifen was first marketed in the US, there have been 159 cases of uterine sarcoma reported worldwide in women taking the drug. The incidence rate of endometrial adenocarcinoma is 2.2 per 1000 women-years versus 0.71 for placebo as observed during long-term follow-up of women enrolled in clinical trials of tamoxifen. The underlying mechanism is unknown, but may be related to the oestrogen-like effect of tamoxifen.

Uterine sarcoma associated with tamoxifen use. Wysowski DK. New England Journal of Medicine. 6 June 2002, 346 (23): 1832-33