Oncologic Staging with Ga-FAPI PET/CT Demonstrates a Lower Rate of Nonspecific Lymph Node Findings Than F-FDG PET/CT.

Nonspecific lymph node uptake on F-FDG PET/CT imaging is a significant pitfall for tumor staging. Fibroblast activation protein α expression on cancer-associated fibroblasts and some tumor cells is less sensitive to acute inflammatory stimuli, and fibroblast activation protein-directed PET may overcome this limitation. Eighteen patients from our prospective observational study underwent F-FDG and Ga fibroblast activation protein inhibitor (FAPI) PET/CT scans within a median of 2 d (range, 0-22 d). Lymph nodes were assessed on histopathology and compared with SUV measurements. On a per-patient basis, lymph nodes were rated malignant in 10 (56%) versus 7 (39%) patients by F-FDG PET/CT versus Ga-FAPI PET/CT scans, respectively, with a respective accuracy of 55% versus 94% for true lymph node metastases. Five of 6 (83%) false-positive nodes on the F-FDG PET/CT scans were rated true negative by the Ga-FAPI PET/CT scans. On a per-lesion basis, tumor detection rates were similar (85/89 lesions, 96%). Ga-FAPI PET/CT imaging demonstrated higher accuracy for true nodal involvement and therefore has the potential to replace F-FDG PET/CT imaging for cancer staging.