Heterogeneity of estrogen binding sites in breast cancer: morphologic demonstration and relationship to endocrine response.

Breast cancer specimens from 184 patients were analyzed for estrogen binding by two different histochemical techniques using conjugates of estradiol, bovine serum albumin, and fluorescein. In one conjugate estradiol was bound at position 6, in the other at position 17. Results were in agreement in 64% (p less than .001), but obvious differences in ligand distribution were noted. Results were also correlated with estrogen receptor (ER) analysis by dextran-coated charcoal assay (DCC) and were in accord in 65% and 67% of specimens respectively (p less than .001). In 114 cases, the tissue samples were also studied with the estrogen receptor immunocytochemical assay (ERICA) of Greene and his colleagues, which employs monoclonal antibodies to ER protein. Results were in accord with DCC in 86% (p less than .001). The pattern of staining with ERICA differed from that of either histochemical method. In 43 cases assay results were correlated with clinical endocrine response. Overall, the best statistical prognostic parameters were obtained with ERICA. Analysis of combined assay results revealed that patients with assays positive by all techniques were the most likely to respond to hormonal treatment (p less than .001), whereas if one or more assays were negative the chances for a good response were significantly less favorable. These data suggest that DCC and ERICA are both a measure of the same estrogen binding site (type I) while the histochemical methods apparently identify two other separate and distinct sites (putative type II sites). A degree of positive interaction may exist between these multiple estrogen binding sites.