Isoelectric focusing of oestradiol receptor protein from human mammary carcinoma--a comparison with dextran coated charcoal assay.

Two simple methods for the detection of specific oestradiol--17 beta protein in breast tumour tissue were investigated. Isoelectric focusing of receptor protein in polyacrylamide gel was examined as an alternative micromethod to dextran-coated charcoal receptor assay. In a series of 32 cytosols prepared from unselected breast tumour tissue, assay results agreed on the presence or absence of receptors in 97% of cases. Quantitative analysis of the positive results showed a correlation coefficient, r = 0.88. Isoelectric focusing gave significantly lower receptor concentrations than the dextran-coated charcoal method. Twenty-six Tru-Cut biopsy tumour specimens were analyzed for receptor by isoelectric focusing and the results were compared with those obtained by the dextran-coated charcoal method on the same tumour. In 88% of the specimens examined, both methods agreed as to the presence or absence of receptor protein. A correlation coefficient, r = 0.62, was calculated from the 15 positive results. There was no significant difference between the results from the two methods. Quantitative results were related to total protein concentration in the cytosol. Negative receptor status was defined as less than 5 fmol/mg cytosol protein for both methods.