Characterization of Laboratory Working Standard for Quality Control of Immunometric and Radiometric Estrogen Receptor Assays. Clinical Evaluation on Breast Cancer Biopsies

The objective of the study was to characterize a low-cost and reliable working standard material for quality control of estrogen receptor (ER) determination with dextran-coated charcoal (DCC) and enzyme immunoassay (EIA) methods. Human fibromatous uterine lyophilized cytosol demonstrated good characteristics of stability and applicability for this purpose. Eleven laboratories participated in the intralaboratory and interlaboratory quality control study, and they achieved slightly higher coefficients of variation for ER-EIA (interlaboratory, 37.7 %; intralaboratory, 22.9 %) than for ER-DCC (Interlaboratory, 24.2 %; intralaboratory, 15.7 %). There was an excellent correlation between ER results with ER-EIA and ER-DCC for 268 breast cancer biopsies. Quality assurance for ER assays using DCC techniques and immunometric methods with monoclonal antibodies (ER-EIA) can be set up with this available material of human origin to satisfy the characteristics of both techniques and the species specificity of monoclonal antibodies.