Uterine side effects of treatment with tamoxifen

Objective: To assess a causal the relationship between endometrial lesions and tamoxifen therapy in patients with breast cancer. Design: Prospective l ongitudinal study and cross-sectional study. Setting: Cancer prevention uni t at Basurto Hospital, Bilbao. Population and methods: Three populations of breast cancer were studied: 43 before the beginning of tamoxifen; 78 after 5-72 months of tamoxifen, and 34 before tamoxifen and after 12-24 months o f tamoxifen treatment (PAIRED GROUP). All of them were systematically, stud ied with CO2 diagnostic hysteroscopy and endometrial biopsy by the same cli nician. Results: Before tamoxifen, the following endometrial lesions were d etected: endometrial polyps 9.3%; endometrial cysts 16.3%; synechiae 11.6%. In the paired group the ingestion of tamoxifen shows a direct causal effec t with a significant increase in endometrial polyps (11.8% vs. 29.4%; OR = 13; CI = 7.9-18.1), in endometrial cysts (17.7% vs. 55.9%; OR = 7.5; CI = 5 .9-9.1) and in synechiae (14.7% vs. 35.5%; OR = 8; CI = 4.7-11.3). In the g roup under tamoxifen for 5-72 months, one endometrial carcinoma was detecte d. Conclusions: Breast cancer patients have a number of endometrial lesions before undergoing any hormonal therapy. Tamoxifen significantly increased benign endometrial lesions, usually after less than one year of treatment. No cases of endometrial carcinoma was found in our series of 34 patients wi th 1-2 years of tamoxifen treatment, and 1/78 in patients with 5-72 months of tamoxifen. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.