Immunocytochemical detection of progesterone receptor in breast carcinoma. Comparison of two monoclonal antibodies.

Immunocytochemical progesterone receptor (PR) assays employing two different monoclonal antireceptor antibodies (mPRi, JZB39) were compared with each other and with the dextran-coated charcoal assay (DCC) in human breast carcinoma. The immunocytochemical analyses were semiquantitatively scored (histoscore) based on relative staining intensity and the percentage of positively stained carcinoma cell nuclei. The immunocytochemically determined PR status agreed with that obtained by the DCC assay in 76% of the cases when the monoclonal antibody mPRi was used. The agreement was slightly better (82%) with the immunocytochemical assay using the JZB39 antibody. The semiquantitative histoscores correlated significantly with log-transformed cytosol PR concentrations in the DCC assay (mPRi, R = 0.543; JZB39, R = 0.618; P less than 0.0001 for both). The histoscores obtained with the mPRi and JZB39 antibodies were highly correlated with each other in adjacent frozen sections (R = 0.84, P less than 0.0001) the latter antibody giving somewhat higher histoscores. These results further validate the use of immunocytochemical PR assays for routine diagnostic purposes, especially when sufficient material is not available for DCC assays.