In A549-FAPI xenografted tumors, stable retention of radioactivity was observed with SUV values greater than 0.4 within 90 min, and this uptake can be effectively blocked by the pre-injection of the cold reference standard (compound 3, 2 mg/kg) with significant inhibition of tumor SUV values (lower than 0.2, over 50% inhibition), indicating the selectivity of [18F]3 to FAP. The gene discussed is FAP; the disease is neoplasm.