The main reason is that FAPIs target a dynamic protein expressed in cells of the tumor microenvironment, unlike other radioligands that target highly expressed proteins on the surface of cancer cells in a specific malignancy type, such as the prostate-specific membrane antigen (PSMA) and the somatostatin receptors in advanced prostate cancer and neuroendocrine tumors, respectively. The gene discussed is FOLH1; the disease is prostate cancer.