p504s, also known as α-methylacyl coenzyme A racemase (AMACR), is an enzyme localized in the peroxisome and mitochondria, which functions in β-oxidation of branched chain fatty acids, as well as bile synthesis. AMACR has been clinically indicated as a tissue biomarker for prostate cancer and colorectal cancer, as well as high-grade prostatic intraepithelial neoplasia, a precursor lesion of prostate cancer. p504s overexpression has also been detected in a number of other cancers including ovarian, breast, bladder, lung, and renal cell carcinomas, lymphoma, and melanoma.