The clinical significance of estrogen receptor (ER) levels determined in breast cancer tissue depends on the quality of the ER assay procedure itself as well as on several critical factors beyond the direct responsibility of the receptor laboratory. A novel immunobiochemical assay (ER-EIA) has been made available by Abbott Laboratories. In comparison to the classical radioligand binding assay, the use of ER-EIA resulted in lower intra- and interassay as well as interlaboratory coefficients of variation. This may be explained by the complete standardization of ER-EIA as compared to ER radioligand binding assay. Considerable attention must be paid to the source of origin of quality control material if identical ER levels are to be obtained by both methods, as the monoclonal antibodies of ER-EIA bind less avidly to cytosolic ER of calf uterus and, in contrast to routine ER radioligand binding assay, are able to recognize occupied ER.

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Presented at the Symposium on “Estrogen Receptor Determination with Monoclonal Antibodies,” December 14, 1984, Monte Carlo.

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