Estradiol receptor analysis in human breast cancer tissue by isoelectric focusing in polyacrylamide gel.

Isoelectric focusing in polyacrylamide gel combined with limited proteolysis is a simple and specific method for quantitation of estradiol receptors in breast cancer tissue. At least eight different samples can be analyzed simultaneously on one gel, and the whole procedure, including sample preparation, takes less than 7 hr. In comparison with sucrose gradient centrifugation, isoelectric focusing is more sensitive, possibly due to the short time (1.5 to 2 hr) needed for the analysis. Furthermore, only one incubation with tritium-labeled estradiol is needed for an analysis, which means that a smaller amount of tumor tissue is needed than for most other methods. This fact allows analysis of the estrogen receptor content in tumor material obtained from fine-needle biopsy.