Effects of tamoxifen on uterus and ovaries of postmenopausal women in a randomised breast cancer prevention trial.

Randomised, double-blind controlled trials have been started to determine whether tamoxifen can prevent or delay development of breast cancer in healthy women with a family history of the disease. We recruited a randomised cohort of 111 postmenopausal women (aged 46-71 years) from the Pilot Breast Cancer Prevention Trial at the Royal Marsden Hospital to study the effect of tamoxifen on the uterus and ovaries. The main outcome measures were obtained by transvaginal ultrasonography with colour doppler imaging and microscopic examination of endometrial biopsies removed at the time of the scan. There was no significant difference between tamoxifen (20 mg/day) and placebo groups in the age of the women, or the time of the scan (and sampling) after randomisation. Women taking tamoxifen had a significantly larger uterus and a lower impedance to blood flow in the uterine arteries. 39% of women taking tamoxifen had histological evidence of an abnormal endometrium compared with 10% in the control group. 10 patients in the tamoxifen group (16%) had atypical hyperplasia and another 5 (8%) had a polyp. Women with a histological abnormality had a significantly thicker endometrium and a decreased impedance to blood flow in the uterine arteries. There was no correlation between the presence of uterine abnormalities and the age of the women, or the concentrations of tamoxifen or desmethyl tamoxifen in the peripheral blood. These findings confirm that tamoxifen can cause potentially malignant changes in the endometrium of postmenopausal women. Transvaginal ultrasonography can be used to identify those women who should have endometrial samples removed for microscopic analysis.