Role of Gallium 68 fibroblast activation protein inhibitor PET/CT in the initial evaluation of gastric adenocarcinoma: a single-institution retrospective study

Objective This study aimed to assess the detection rate of gallium 68 (Ga-68) fibroblast activation protein inhibitor (FAPI) PET/computed tomography (CT) for primary and metastatic gastric adenocarcinomas and to correlate quantitative tracer uptake with different histopathological subtypes. Methods A single-center retrospective observational study was conducted on 90 adult patients with histopathologically proven gastric adenocarcinoma. All patients underwent Ga-68 FAPI PET/CT for initial staging before therapy. The detection rate of primary tumors and the incidence of metastases were evaluated. Semiquantitative parameters, including maximum standardized uptake value (SUV max ) and tumor-to-background ratio (TBR), were correlated with histopathology using the Kruskal–Wallis test. Results Ga-68 FAPI PET/CT demonstrated a 100% detection rate for primary gastric tumors, with a median SUV max of 11.81. The uptake was not significantly influenced by histopathological subtype ( P = 0.437). Distant metastases and peritoneal carcinomatosis were detected in 52.2 and 46.7% of patients, respectively. High tracer uptake was observed even in subcentimetric peritoneal lesions. Notably, distant parenchymal metastases without peritoneal or regional involvement were detected in five (5.5%) patients. No adverse events were reported. Conclusion Ga-68 FAPI PET/CT shows high tracer uptake and excellent tumor-to-background delineation, with its uptake being independent of histological subtype. The modality is highly effective for detecting peritoneal and distant metastases, including otherwise occult sites of disease, which could potentially impact management decisions. These findings suggest that Ga-68 FAPI PET/CT may become a valuable tool for the staging of gastric cancer; however, the retrospective design and lack of comparison with FDG PET/CT are limitations requiring further validation in prospective multicenter studies.