Prostate-specific acid phosphatase (PSAP) is an enzyme produced in prostate epithelial cells. PSAP expression levels proportionally increase with prostate cancer progression (1). PSAP IHC staining is often used in conjunction with prostate specific antigen (PSA) staining to help distinguish poorly differentiated carcinomas. For instance, PSAP is commonly used to help differentiate prostate adenocarcinoma and urothelial carcinoma which may appear microscopically similar; prostate adenocarcinoma often stains with PSA and/or PSAP, while urothelial carcinoma does not (2). PSAP has a significantly higher correlation with the morphological characteristics of prostate cancer and can provide a more accurate predictive prognosis than other markers currently available. Since PSAP detection is a proportional measure of prostate cancer progression, it can also be used as an immunotherapy target for treatment of prostate cancer (1). Due to its prostate specificity, PSAP may also be a useful marker for excluding metastases from a prostatic primary, particularly in male breast cancer (3).