Estrogen receptor levels in hormonally progressive mammary tumors

Tumor samples from 4 different stages of hormonal progression in the MT‐W9 series of rat mammary tumors were analyzed for estrogen receptors by the dextran‐coated charcoal method in order to further explore the clinical implications of the estrogen receptor assay. The findings indicate that although the presence of estrogen receptors is not an exclusive characteristic of hormonal dependency, their absence is indicative of a later stage of hormonal progression which might be of more immediate clinical consequence because hormonally autonomous tumors have faster growth rates than hormonally dependent tumors. It is also suggested that it may be necessary to initiate chemotherapy as an adjuvant to endocrine therapy for metastatic breast cancer patients with hormonally dependent tumors in order to avoid the eventual proliferation of hormonally autonomous tumor cells which are present in hormonally dependent tumors.