Quantitation of estrogen receptors in human breast cancer by agar gel electrophoresis.

Samples from human primary and metastatic mammary carcinomas were examined for the presence of specific estrogen-binding proteins. Cytosols were incubated with [3H]estradiol-17beta with and without an excess of unlabelled estradiol or estrogen antagonist. After incubation, the mixtures were treated with dextran-charcoal to remove non-specifically bound steroid. Low-temperature agar gel electrophoresis was used to separate receptor- and non-receptor-bound steroid. Statistically significant differences were found between the tissue protein contents of primary mammary carcinomas and skin metastases. Estrogen receptor and tissue protein contents of the tumors seem to be related to the age of the patients. Objective remissions with endocrine therapy were obtained in patients with carcinomas which possessed a substantial concentration of estrogen receptors.