FOLH1 and metastatic prostate carcinoma: PSMA is a transmembrane enzyme that has low levels of expression in normal prostate, kidney, and small intestine tissue, as well as salivary and lachrymal glands, but is overexpressed by 100- to 1000-fold in over 90% of metastatic prostate cancers, with particularly elevated levels in mCRPC [8,9,10].