Nuclear binding of the estrogen receptor: a potential predictor for hormone response in metastatic breast cancer.

We have previously described an in vitro immunohistochemical test employing anti-receptor antibodies, for demonstrating the nuclear binding characteristics of estrogen receptors (ER) in breast carcinomas. Based on a retrospective analysis of twenty-five patients with estrogen receptor-positive (ER+) breast cancer who were treated with hormone therapy and whose clinical responses were evaluable, we were able to demonstrate that this test may be valuable to predict which, among the ER+ tumors (whether or not they are progesterone receptor positive, PR+), are likely to respond to hormone therapy and which may fail. While tumors in which ER exhibited abnormalities in nuclear binding behavior (ligand-independent nuclear binding or no nuclear binding) failed hormone therapy (16 out of 19 patients), those in which nuclear binding of ER appeared normal (ligand-dependent) in the in vitro test, responded to hormone therapy (5/6 patients). While our previous report dealt with the procedural details, specificity of the reagents, and the design of the study, this report addresses the clinical aspects of this study and response correlation.