Tamoxifen-stimulated growth of human endometrial carcinoma.

An estrogen receptor and progesterone receptor positive endometrial carcinoma (EnCa101) will grow in response to either estradiol or tamoxifen when transplanted into athymic mice. We have tested several antiestrogens with different properties to determine their ability to support endometrial tumor growth. Trioxifene, enclomiphene and nafoxidine are all as active as tamoxifen whereas the antiestrogen keoxifene, that has reduced estrogen-like properties, will partially inhibit tamoxifen-stimulated growth. Furthermore, the pure antiestrogen ICI 164,384 will block tamoxifen-stimulated growth without having any effect itself on tumor growth rate. Overall, the ability of antiestrogens to stimulate the growth of human endometrial carcinoma EnCa101 appears to be related to their intrinsic estrogenic activity.