Evaluation of a new oestrogen receptor assay

Replicate assays of oestrogen receptor (ER) concentration on 81 specimens of human breast carcinoma were performed to compare the ligand binding Sephadex separation method with a polystyrene bead linked anti-oestrogen receptor monoclonal antibody technique (enzyme immunoassay [EIA], Abbott Laboratories). Each specimen was homogenized and the cytosol divided into four fractions. Replicate assays by each method gave an estimate of reproducibility. The mean CV (coefficient of variation = standard deviation/mean) for the ligand binding method was 9.73% compared with a mean CV of 17.9% for the EIA method. In the clinically significant range of ER values, around the cut-off point between negative and positive assays, there was no difference in the precision of the two assays (Mann Whitney U-test). The correlation between methods gave a Pearson's Product Moment Correlation Coefficient (r value) of 0.822, significant at the P less than 0.001 level, indicating a close correlation between the two methods. The highest CVs for both methods were in the range of oestrogen receptor concentrations, below 10 fmol/mg cytosol protein. Using 10 fmol/mg cytosol protein as a cut-off between negative and positive assays, 9.87% of the specimens would be reclassified as either positive or negative by the new assay method. The new assay method is, therefore, acceptable for clinical use.