Whither cytosolic estrogen receptor assays? A comparison of commercially available kits for estrogen receptor assay.

Frozen tissue sections and cytosols from 89 specimens of breast and ovarian tumours have been assayed for the presence of estrogen receptor (ER) or related protein using four commercially available monoclonal antibody methods. These were estrogen receptor enzyme immunoassay (ER-EIA), estrogen receptor enzyme immunocytochemical assay (ER-ICA), ER D5 antigen immunoradiometric assay and ER D5 antigen immunocytochemical assay. The results have been compared with those obtained using a standard dextran coated charcoal steroid binding assay (ER-DCC). The correlation coefficient (r) between ER-DCC and ER-EIA results was 0.72 while that of both monoclonal antibody cytosol methods and their respective immunocytochemical assays was 0.66. ER-ICA gave additional valuable information concerning receptor heterogeneity in breast cancer sections. However, the correlation between ER D5 antigen assays and both ER-DCC and ER-EIA was weak (r less than 0.4). We conclude that there are a number of methodological advantages in using the kit systems including their ability to detect receptor presence in small tumour specimens (e.g., "Tru-cut" biopsies) but that their usefulness is limited by the current lack of widely available monoclonal based methods for the concurrent determination of progestogen receptor. We believe that, once these are available, immunocytochemical technology could offer an alternative method of determining the steroid receptor concentration in both ovarian and breast tumours, thus obviating the need for costly and time-consuming cytosolic methods, with their inherent difficulties of quality control.