[68Ga]-FAPI-04 outperforms [18F]-FDG in gastric cancer staging: a comparative study using PET/CT and PET/MR

Purpose This study aimed to systematically compare the diagnostic performance of gallium-68–labeled fibroblast activation protein inhibitor-04 ([ ⁶⁸ Ga]-FAPI-04) and fluorine-18 fluorodeoxyglucose ([ ¹⁸ F]-FDG) for gastric cancer staging using positron emission tomography combined with computed tomography (PET/CT) and positron emission tomography combined with magnetic resonance imaging (PET/MR). Methods In this single-center retrospective study, 35 patients with pathologically confirmed gastric cancer underwent sequential imaging with [ ⁶⁸ Ga]-FAPI-04 (PET/CT and PET/MR) and [ ¹⁸ F]-FDG (PET/CT and/or PET/MR) within 48 hours. Diagnostic performance for primary tumors, lymph node metastases, and distant metastases was evaluated against histopathological results or clinical follow-up. Semi-quantitative parameters, including maximum standardized uptake value (SUV _max ) and target-to-background ratio (TBR), were compared across tracers and modalities. Results [ ⁶⁸ Ga]-FAPI-04 exhibited significantly higher SUV _max and TBR than [ ¹⁸ F]-FDG in primary tumors, lymph node and peritoneal metastases. Notably, [ ⁶⁸ Ga]-FAPI-04 maintained consistently high uptake in signet-ring cell carcinoma, a subtype where [ ¹⁸ F]-FDG uptake was significantly lower. [ ⁶⁸ Ga]-FAPI-04 PET/MR achieved 100% sensitivity and specificity for peritoneal metastases, significantly outperforming all [ ¹⁸ F]-FDG-based modalities. While whole-body PET/CT yielded higher absolute SUV _max values, PET/MR demonstrated superior performance in terms of TBR. Conclusion [ ⁶⁸ Ga]-FAPI-04 outperforms [ ¹⁸ F]-FDG in visualizing primary and metastatic gastric cancer lesions. The combination of [ ⁶⁸ Ga]-FAPI-04 and PET/MR is a particularly effective imaging strategy, delivering superior diagnostic performance for detecting peritoneal metastases and evaluating [ ¹⁸ F]-FDG-insensitive subtypes, thereby optimizing precise staging.