Our investigation focused on: (i) quantifying FAP expression in healthy and PC3-mice as well as in blood; (ii) comparing these values with the uptake of the FAPI radiotracers in tumor, blood and organs; (iii) performing a dose escalation and in vivo selectivity investigation to assess the impact of sFAP, PREP and DPP-4 on the efficacy of the FAPI-radiotracers. Here, DPP4 is linked to neoplasm.