Immunocytochemistry In the Assessment of Ps2 Protein Expression In Fine Needle Aspiration Cytology From Breast Carcinoma

pS2 protein is a cysteine‐rich polypeptide, of unknown function, the expression of which is induced in the human cancer cell line MCF‐7 by oestrogen. the availability of a murine monoclonal antibody to human pS2 protein has prompted us to evaluate its expression in 47 cases of primary breast carcinoma. Using a double indirect immunoperoxidase technique, we compared the expression of pS2 protein in fine needle aspiration (FNA) cytology smears with that in formalin‐fixed, paraffin‐embedded sections from subsequently excised tumours from the same patients. We also compared the expression of pS2 protein and oestrogen receptor (ER) status using immunocytochemical assay (ER‐ICA) in formalin‐fixed, paraffin‐embedded sections from 22 primary breast carcinomas. We found the application of immunocytochemistry in the assessment of pS2 protein expression in FNA cytology to be a reliable and cost‐effective technique, having a sensitivity of 84% and a specificity of 100%. There was also a good correlation between the expression of pS2 protein and ER status.