P504S (AMACR) is an enzyme in the beta-oxidation of branched-chain fatty acids. Expression of P504S protein is found in prostatic adenocarcinoma but not in benign prostatic tissue. It has also been found to stain premalignant lesions of the prostate: high-grade prostatic intraepithelial neoplasia (PIN) and atypical adenomatous hyperplasia. P504S can be used as a positive marker for PIN. It may be useful to confirm the diagnosis of small focus of prostate carcinoma in needle biopsies. P504S stains the vast majority prostate cancer, however, P504S has been shown to stain numerous other types of carcinoma such as hepatoma, breast carcinoma, pancreatic islet tumor and desmoplastic small round cell tumor.