It is worth noting that the FAPI-specific PET/CT imaging in thyroid cancers with a flip-flop phenomenon on 18F-FDG PET/CT, metastatic castration-resistant prostate cancers with non-PSMA-avid metastases in 68Ga-PSMA PET/CT, and unknown primary tumors may be interesting subjects for further investigations. The gene discussed is FOLH1; the disease is thyroid gland carcinoma.