Estrogen receptor immunocytochemical assay (ER-ICA): computerized image analysis system, immunoelectron microscopy, and comparisons with estradiol binding assays in 115 breast carcinomas.

An estrogen receptor (ER) immunocytochemical assay (ER-ICA) was applied to 115 malignant breast carcinomas and the results were compared to those of steroid binding assays performed on cytosol extracts of the same tumors. Immunoperoxidase (peroxidase-antiperoxidase) staining was performed on frozen sections using rat monoclonal antibody to estrogen receptor H222SP gamma. A preembedding method was used for the immunoelectron microscopy study. A semiquantitative analysis and a computerized image analysis system (SAMBA 200 TITN) were used to evaluate the positive ER immunostaining. Positive immunostaining (81 of 115) was always located in the nucleus of tumor cells and of normal cells in adjacent breast tissue. The immunostaining pattern differed from one tumor to another, due to variations in either the intensity or the percentage of positive cells. When immunohistochemical staining was correlated to biochemical assay, there was an 88% correlation, and staining intensity and percentage of positive cells significantly increased (P less than 0.01) with cytosolic ER levels and were independent of cellularity. These results indicated that ER-ICA is to date the most reliable histochemical method for ER detection and correlated in 88% of the cases with ER biochemical assay; ER-ICA constitutes a method particularly valuable to screen ER negative tumors on condition that tumor fragment quality (sampling and storage) is perfectly controlled; ER-ICA provides additional information for heterogeneous ER distribution within tumors; ER-ICA as a qualitative method is unable to replace the quantitative ER determination obtained with biochemical assay although the computerized system (SAMBA 200) for image analysis of microscopic preparations constitutes a valuable improvement of immunostaining analysis; and ER-ICA based on ER antigenic site detection is complementary to biochemical assay based on ER functional site determination.