Innnunohistochemical Measurement of Estrogen Receptors in Breast Cancer Tissue Samples1

A new estrogen receptor immunocytochemical assay (ER-ICA) which uses monoclonal antibodies to the estrogen receptor protein was applied to 97 breast cancer tissues. The results were correlated to those obtained by conventional dextran coated charcoal assays. The presence or absence of nuclear staining was significantly associated with positive or negative estrogen receptor status by dextran-coated charcoal (/' < 0.001). Fur thermore ER-ICA results showed a high degree of correlation with a light microscopic grading. The relationship between ER-ICA results and response to endocrine therapies in patients with advanced disease was assessed in 20 patients. Six of 11 (55%) ER-ICA positive patients responded, whereas 8 of 9 (89%) ER-ICA negative patients failed.