Influence of hormones on proliferation of ER-positive cells and ER-negative cells of human breast cancer (MCF-7).

The influence of endocrine therapy on the proliferation of estrogen receptor (ER)-positive cells and ER-negative cells of human breast cancer (MFC-7) serially transplanted into nude mice was analyzed by tumor growth, dextran-coated charcoal (DCC) method, ER-immunocytochemical assay (ER-ICA) and ER-immunocytochemically stained 3H-thymidine autoradiography. In the tamoxifen (TAM) group and the medroxyprogesterone acetate (MPA) group, tumor growth was inhibited, but it was promoted in the 17-beta-estradiol dipropionate (E2) group. The ER level by the DCC method was significantly decreased in the TMA, the MPA and the E2 groups. The ER-ICA showed that the percentage of ER-positive cells was decreased in the TAM and the MPA group, but it was increased in E2 group. However, the ER-immunocytochemically stained 3H-thymidine autoradiography showed that not only the labelling index of ER-positive cells but also that of ER-negative cells was significantly decreased in the TAM and the MPA groups, while the labelling index was significantly increased in the E2 groups. Therefore, it was concluded that endocrine therapy affected the proliferation of both ER-positive cells and ER-negative cells of ER-positive breast cancer.