Impact of 68 Ga-FAPI-PET/CT imaging on the therapeutic management of primary and recurrent pancreatic ductal adenocarcinomas.

Purpose: Pancreatic ductal carcinoma (PDAC) is a highly lethal cancer and early detection and accurate staging are critical to prolonging survival. PDAC typically has a prominent stroma including cancer-associated fibroblasts (CAFs) that express Fibroblast Activation Protein (FAP). FAP is a new target molecule for PET imaging of various tumors. In this retrospective study we describe the clinical impact of PET/CT imaging using 68 Ga-labelled FAP-Inhibitors (68 Ga-FAPI - PET/CT) in 19 patients with PDAC (7 primary, 12 progressive/recurrent). Patients and Methods: All patients have undergone contrast enhanced Computed Tomography (ceCT) for TNM staging before they were subjected to 68 Ga-FAPI - PET/CT imaging. PET-scans were acquired 60 minutes after administration of 150-250 MBq of 68 Ga-labelled FAP-specific tracers. In order to characterize 68 Ga-FAPI-uptake over time, additional scans after 10 minutes and/or 180 minutes were performed in six patients. SUVmax and SUVmean values of PDAC manifestations and healthy organs were analyzed. The tumor burden according to 68 Ga-FAPI - PET/CT was compared to TNM staging based on ceCT and changes in oncological management were recorded. Results: Compared to ceCT, 68 Ga-FAPI - PET/CT results led to changes in TNM staging in 10/19 patients. 8/12 patients with recurrent/progressive disease, were up-staged, 1 down-staged and 3 had no change. In newly diagnosed PDAC, 1/7 patients was up-staged, the staging of 6 patients did not change. Changes in oncological management occurred in seven patients. Markedly elevated uptake of 68 Ga-FAPI in PDAC manifestations after 1 hour was seen in most cases. Differentiation from pancreatitis based on static imaging 1 hour p.i. was challenging. With respect to imaging after multiple time points, PDAC and pancreatitis showed a trend for differential uptake kinetics. Conclusion: 68 Ga-FAPI - PET/CT led to restaging in half of patients with PDAC and most patients with recurrent disease compared to standard of care imaging. The clinical value of 68 Ga-FAPI - PET/CT should be further investigated.