FOLH1 and prostate cancer: PET and SPECT radiotracers have been developed to target specific markers on cancer cells that are upregulated relative to healthy tissue; notably PSMA, which is often overexpressed in prostate cancer 6,7, the somatostatin receptor 2 (SSTR2) which is commonly overexpressed on neuroendocrine tumors 8, and the fibroblast activation protein (FAP) 9, which is overexpressed in various tumor microenvironments.