Relationship between ER-ICA and conventional steroid receptor assays in human breast cancer

We applied a new immunocytochemical assay for estrogen receptors (ER-ICA) to 82 human breast tumors. Results were correlated with cytosolic estrogen receptors (ERc) and nuclear ER (ERn) determined on the same sample respectively by the radioligand binding assay and by an ER enzyme immunoassay (ER-EIA). All ER-ICA-positive tumors contained more than 10 fmol/mg of protein of ERc and were therefore considered as ERc positive. In contrast, 15.4% of ERc-positive cases were ER-ICA negative. Comparison of ER-ICA results with ERn showed extensive agreement of negativity (92%), whereas 38% of ER-ICA-positive tumors were ER-EIA negative. However, the latter had ERc levels above the positivity threshold. Quantitative features of the immunocytochemical staining such as intensity and percentage of labelled cells, considered separately, did not reflect the amount of ERc or ERn. Cellularity was not significantly correlated with ER-ICA and biochemical results.