Immunohistologic localization of estrogen receptors in breast cancer with monoclonal antibodies. Correlation with biochemistry and clinical endocrine response.

Breast cancer specimens from 114 patients were assayed for the presence of estrogen receptors (ER) utilizing highly specific, monoclonal antiestrophilin antibodies and the peroxidase-antiperoxidase technique. Results were compared with conventional ER determinations by the dextran-coated charcoal method (DCC) and were in agreement as to positivity and negativity in 86%. Semiquantified immunocytologic assay results were in accord with the level of ER as measured by DCC in 66%. The tumors studied included 43 from patients with Stage IV disease where clinical response to hormonal manipulation was known. In the latter group, the immunohistologic method had a sensitivity similar to that of DCC but showed a superior positive predictive value and a significantly better specificity. These results indicate that this new method is a valuable laboratory tool, enabling prediction of hormone responsiveness in advanced mammary carcinoma and capable of performance at the community hospital level.