Determination of estrogen receptor in breast cancer using monoclonal antibody technology: results of a multicenter study in the United States.

Three laboratories compared their routine steroid binding assays with the Abbott estrogen receptor-enzyme immunoassay (ER-EIA) to determine ER in breast cancer cytosols. Each laboratory was first trained to use the ER-EIA kit and then performed routine proficiency panels to determine assay reproducibility. The frozen panels prepared from MCF-7 cytosol produced good intraassay results but the between assay coefficients of variation were frequently above 10%. Lyophilized MCF-7 cytosols produced better reproducibility upon repeated assay. One laboratory demonstrated that New England Nuclear steroid binding kits and the ER-EIA produced comparable results when MCF-7 lyophilized cytosols were used. The analysis of breast tumor samples demonstrated excellent linear correlation coefficients for each laboratory (greater than 0.92 N approx. 60 samples each) but different slopes. The comparison of the ER-EIA with the New England Nuclear steroid binding assay produced a slope of 1.13. The ER-EIA appears to produce comparable results to the conventional steroid binding assays for the determination of ER in breast tumor cytosols.