PSA is a chymotrypsin-like serine protease (kallikrein family) produced by the prostate epithelium. PSA is used to confirm prostatic acinar cell origin in primary and metastatic carcinomas and to rule out non-prostatic carcinoma mimics. Clone EP1588Y was tested on 167 cases of prostate for specificity and sensitivity and stained 98% of all prostate cancers, (Table). It was found to be slightly more sensitive than a mouse monoclonal PSA [clone ER-PR8]. This antibody is to be used for paraffin-embedded tissue only and is not to be used in serum testing.