P504S is an enzyme in the ß-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 foci
of prostate carcinoma in needle biopsies. P504S stains the majority prostate
cancer, however, P504S has been shown to stain many other types of carcinoma
such as hepatoma, breast carcinoma, pancreatic islet tumor and desmoplastic
small round cell tumor (Miller and Tacha)1. HMW CK and p63 may serve as a useful
panel.