Methods-Endometria from 19 prospectively collected breast cancer patients treated with tamoxifen were ascribed a pathological diagnosis and the findings compared with those in a control group matched for age and presentation. The abnormalities were related to cumulative tamoxifen dose.

Results-The two asymptomatic treated patients had generalised simple endometrial hyperplasia at necropsy. No endometrial abnormalities were seen at necropsy in the two control cases. Of the 17 patients treated with tamoxifen who underwent surgery for gynaecological symptoms, 11 had hyperplastic endometrial polyps characterised by epithelial metaplasias and patchy periglandular condensation of stroma. Two women had primary endometrial malignancies with myometrial invasion, and three women, one of whom had previously presented with a benign polyp, had an endometrial polyp-cancer on a background of hyperplasia. Endometrial malignancies were confined to women who had taken more than 35 g of tamoxifen. The control group included no endometrial polyp-cancers, only one patient with an endometrial polyp, four women with endometrial hyperplasia and four with primary endometrial malignancy.

Conclusions-These findings support a link between prolonged tamoxifen treatment and endometrial malignancy and identify a subgroup of patients-that is, those who have taken more than 35 g of tamoxifen, who may be at increased risk of endometrial cancer. The spectrum of pathological findings in patients treated with tamoxifen suggests that the drug promotes endometrial growth and that endometrial polyps may be an important intermediate step in endometrial carcinogenesis.