Estrogen receptor assay: Interlaboratory and intralaboratory variations in the measurement of receptors using dextran-coated charcoal technique: A study sponsored by E.C.O.G.

Abstract

Six laboratories performing estrogen receptor analysis in breast cancer for patients included in clinical protocols of the Eastern Cooperative Oncology Group participated in a quality control study for estrogen receptor assay. Three tissue powders containing 10–50 femtomoles of estrogen receptors/mg cytosol protein were distributed and the results analyzed for interlaboratory and intralaboratory variations. Frequency of misclassification of the receptor-positive powders as receptor-negative was related to the quantity of receptors. All labs except one were able to distinguish “low content” from “medium content” and the “medium” from the “high content” powders despite the variability in the numerical values reported for the powders. Two of the six labs reported consistently low values for all samples and the results of one lab were consistently higher than the average of the values obtained for the powders. These results could not be explained by the variations in protein content reported by these laboratories for different powders. Implications of the degree of inter-lab and intra-lab variations in the assay results are discussed with reference to their effect on selecting patients for hormonal vs chemotherapy. Based on the results of this study, tentative suggestions for quality control for the receptor assay are also made.