Utility of [(68)Ga]FAPI-04 and [(18)F]FDG dual-tracer PET/CT in the initial evaluation of gastric cancer

OBJECTIVES: We aimed to investigate the role of [(68)Ga]FAPI-04 and [(18)F]FDG dual-tracer PET/CT for the initial assessment of gastric cancer and to explore the factors associated with their uptake. METHODS: This study enrolled 62 patients with histopathologically confirmed gastric cancer. We compared the diagnostic performance of [(68)Ga]FAPI-04, [(18)F]FDG, and combined dual-tracer PET/CT. The standardized uptake value (SUV) and tumor-to-background ratio (TBR) were also measured, and the factors that influence tracer uptake were analyzed. RESULTS: [(68)Ga]FAPI-04 PET/CT detected more primary lesions (90.3% vs 77.4%, p = 0.008) and peritoneal metastases (91.7% vs 41.7%, p = 0.031) and demonstrated higher SUV(max) and TBR values (p < 0.001) of primary lesions compared to [(18)F]FDG PET/CT. Dual-tracer PET/CT significantly improved the diagnostic sensitivity for the detection of distant metastases, compared with stand-alone [(18)F]FDG (97.1% vs 73.5%, p = 0.008) or [(68)Ga]FAPI-04 (97.1% vs 76.5%, p = 0.016) PET/CT. Subsequently, treatment strategies were changed in nine patients following [(68)Ga]FAPI-04 and [(18)F]FDG dual-tracer PET/CT. Nevertheless, [(68)Ga]FAPI-04 uptake was primarily influenced by the size and invasion depth of the tumor. Both [(68)Ga]FAPI-04 and [(18)F]FDG PET/CT showed limited sensitivity for detecting early gastric cancer (EGC) (37.5% vs 25.0%, p > 0.05). CONCLUSIONS: In this initial study, [(68)Ga]FAPI-04 and [(18)F]FDG dual-tracer PET/CT were complementary and improved sensitivity for the detection of distant metastases pre-treatment in gastric cancer and could improve treatment stratification in the future. [(68)Ga]FAPI-04 had limited efficacy in detecting EGC. KEY POINTS: • [(68)Ga]FAPI-04 and [(18)F]FDG dual-tracer PET/CT are complementary to each other for improving diagnostic sensitivity in the initial evaluation of distant metastases from gastric cancer. • [(68)Ga]FAPI-04 PET/CT showed limited sensitivity in detecting EGC. • Need for further validation in a larger multi-centre prospective study. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s00330-022-09321-1.