Oncologic Staging with<sup>68</sup>Ga-FAPI PET/CT Demonstrates a Lower Rate of Nonspecific Lymph Node Findings Than<sup>18</sup>F-FDG PET/CT
Tristan T. Demmert, Kelsey L. Pomykala, Helena Lanzafame, Kim M. Pabst, Katharina Lueckerath, Jens T. Siveke, Lale Umutlu, Hubertus Hautzel, Rainer Hamacher, Ken Herrmann, Wolfgang P. Fendler
Abstract
Nonspecific lymph node uptake on <sup>18</sup>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. <b>Methods:</b> Eighteen patients from our prospective observational study underwent <sup>18</sup>F-FDG and <sup>68</sup>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. <b>Results:</b> On a per-patient basis, lymph nodes were rated malignant in 10 (56%) versus 7 (39%) patients by <sup>18</sup>F-FDG PET/CT versus <sup>68</sup>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 <sup>18</sup>F-FDG PET/CT scans were rated true negative by the <sup>68</sup>Ga-FAPI PET/CT scans. On a per-lesion basis, tumor detection rates were similar (85/89 lesions, 96%). <b>Conclusion:</b><sup>68</sup>Ga-FAPI PET/CT imaging demonstrated higher accuracy for true nodal involvement and therefore has the potential to replace <sup>18</sup>F-FDG PET/CT imaging for cancer staging.