FAP and cancer: The results obtained can be correlated with the three main mechanisms of selective tumor uptake associated with nanoparticles: (1) high uptake in the tumor stroma due to the enhanced permeability and retention (EPR) effect (a passive mechanism); (2) expression of FAP in fibroblasts; and (3) PSMA expression in cancer cells and tumor neovasculature, which involves active mechanisms mediated by receptors present in the tumor stroma that recognize iFAP and iPSMA ligands bound to the surface of the nanoparticles.