⁶⁸Ga-Labeled Fibroblast Activation Protein Inhibitor (⁶⁸Ga-FAPI) PET for Pancreatic Adenocarcinoma: Data from the ⁶⁸Ga-FAPI PET Observational Trial

The fibroblast activation protein (FAP) is highly expressed on carcinoma-associated fibroblasts in the stroma of pancreatic cancer and thus is a promising target for imaging and therapy. Preliminary data on PET imaging with radiolabeled FAP inhibitors (FAPIs) demonstrate superior tumor detection. Here we assess the accuracy of FAP-directed PET in patients with pancreatic cancer. Methods: Of 64 patients with suspected or proven pancreatic cancer, 62 (97%) were included in the data analysis of the ⁶⁸Ga-FAPI PET observational trial (NCT04571086). All of these patients underwent contrast-enhanced CT, and 38 patients additionally underwent ¹⁸F-FDG PET. The primary study endpoint was the association of ⁶⁸Ga-FAPI PET uptake intensity and histopathologic FAP expression. Secondary endpoints were detection rate, diagnostic performance, interreader reproducibility, and change in management. Datasets were interpreted by 2 masked readers. Results: The primary endpoint was met: The association between ⁶⁸Ga-FAPI SUV_max and histopathologic FAP expression was significant (Spearman r, 0.48; P 5 0.04). For histopathology-validated lesions, ⁶⁸Ga-FAPI PET showed high sensitivity and positive predictive values (PPVs) on per-patient (sensitivity, 100%; PPV, 96.3%) and per-region (sensitivity, 100%; PPV, 97.0%) bases. In a head-to-head comparison versus ¹⁸F-FDG or contrast-enhanced CT, ⁶⁸Ga-FAPI detected more tumor on a per-lesion (84.7% vs. 46.5% vs. 52.9%), per-patient (97.4% vs. 73.7% vs. 92.1%), or per-region (32.6% vs. 18.8% vs. 23.7%) basis, respectively. ⁶⁸Ga-FAPI PET readers showed substantial overall agreement on the basis of the Fleiss k: primary k, 0.77 (range, 0.66–0.88). Minor and major changes in clinical management occurred in 5 patients (8.4%) after ⁶⁸Ga-FAPI PET. Conclusion: We confirmed an association of ⁶⁸Ga-FAPI PET SUV_max and histopathologic FAP expression in pancreatic cancer patients.