[Effect of tamoxifen and estrogens on breast cancer cell lines: MCF-7 and R-27, and on the uterus and vagina of fetal and newborn guinea-pigs].

The action of tamoxifen was studied in two models: in breast cancer cell lines MCF-7 and R-27. The latter is resistant to tamoxifen; 2) in the uterus and vagina of guinea pig during the perinatal period. In the breast cancer cell line MCF-7 tamoxifen blocks the proliferation of the cells and in the R-27 it does not antagonize the effects provoked by estrogens. However, in this cell line tamoxifen provokes a significant alteration of the ultrastructures. In the uterus and vagina of guinea pig (fetal and newborn) tamoxifen acts as a real estrogen and it does not block the effects provoked by estrogens.