Immunocytochemical detection of estrogen and progesterone receptors in 124 human breast cancers

Monoclonal antibodies to human estrogen receptor (ER), and rabbit progesterone receptor (PR), also recognizing human PR, were used to detect the receptors by peroxidase immunocytochemistry in frozen sections of 124 primary breast carcinomas. Both ER and PR were almost exclusively located in carcinoma cell nuclei, with heterogeneous distribution and intensity. The staining results were evaluated semiquantitatively (histoscore), based on the percentage of positively stained carcinoma cells and nuclear staining intensity. The receptor status thus determined was as follows: ER+PR+ in 50 patients, ER+PR- in 23, ER-PR- in 26, and ER-PR+ in 3 patients. There was a 79% (ER) or 70% (PR) agreement in the positivity/negativity between the immunocytochemical and steroid-binding assay (in 102 patients) with a highly significant correlation. The histoscore values increased significantly with cytosol receptor levels (ER, r = 0.623, P less than 0.001; PR, r = 0.366, P less than 0.01).