Sucrose density gradient centrifugation and isoelectric focusing were compared as methods for measurement of estrogen receptor protein in human mammary carcinoma. Twenty-six carcinomas were investigated. It is concluded that the micromethod used for isoelectric focusing may be used as a routine tool for estimation of estradiol receptor levels in human mammary carcinoma. With sucrose gradient analysis, control runs are required in which the specific binding sites are displayed by excess of unlabeled ligand. These type of controls were found to be unnecessary with isoelectric focusing. We therefore suggest that isoelectric focusing may be a more specific technique for the detection of estrogen receptor in human mammary carcinoma. Final evaluation of which of these methods is preferable in predictive tests for therapy of breast cancer, however, awaits correlation between measured receptor levels and response to endocrine therapy.
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