Immunocytochemical analysis of progesterone receptors in breast cancer

Breast cancer specimens from 116 patients were assayed for the presence of progesterone receptor (PR), with the use of a highly specific monoclonal antibody and the peroxidase-antiperoxidase technique on cryostat and permanent sections. Results were compared with those obtained by the conventional PR determination by dextran-coated charcoal (DCC) assay; they were in concordance in 90% of cryostat sections and 85% of paraffin-embedded tissue. The sensitivity and specificity of the PR immunocytochemical assay (PR-ICA) were 91% and 89% for frozen sections and 83% and 89% for permanent sections, respectively. The immunostained slides also were evaluated for several semiquantitative features, including staining intensity, heterogeneity of staining, and the proportion of positive tumor cells. A statistically significant correlation was found between the percentage of tumor cells stained with the PR immunocytochemical technique and the PR-cytosol levels (P less than 0.05). These results suggest that the PR-ICA is an effective tool in the evaluation of PR content in breast cancer and can be applied in paraffin as well as frozen sections. This technique provides excellent morphologic detail, as well as tissue localization for PR. It also offers an alternative for assessment of PR when fresh tissue is not available for conventional hormone receptor analysis. The immunocytochemical assay can be performed easily at community hospitals. Because it requires only a small amount of tissue, PR-ICA is an ideal method for analyzing specimens of insufficient size for the DCC assay. This technique also is suited to the evaluation of fine-needle aspiration biopsy specimens.