Comparative analysis of fibroblast activation protein Inhibitor (FAPI) O4 PET/CT versus flurodeoxyglucose (FDG) PET/CT in staging gastrointestinal tumours.

3093 Background: FAPI 04 PET/CT has emerged as a promising alternative to FDG PET/CT, offering potential advantages in sensitivity, specificity, and patient comfort due to its unique targeting of fibroblast activation protein (FAP), which is up regulated in the stromal cells of many cancers. This study aims to evaluate the diagnostic performance of FAPI 04 PET/CT compared to FDG PET/CT for staging gastrointestinal (GI) tumours. Methods: 55 patients with suspected or confirmed GI malignancies underwent both FDG PET/CT and FAPI 04 PET/CT scans within a 7-day window. A total of 115 lesions were identified across the cohort, including colorectal, gastric, pancreatic, and oesophageal cancers. Tumor localization, lesion size, and uptake characteristics were compared between the two imaging modalities. Sensitivity, specificity, and diagnostic accuracy were calculated using histopathology as the gold standard. Results: Of the 55 patients, 31 were male and 24 female, with a median age of 58 years (range: 42–78). FAPI 04 PET/CT demonstrated superior sensitivity (92%) compared to FDG PET/CT (84%) for the detection of GI tumours, particularly in pancreatic and colorectal cancers, where stromal fibrosis is prevalent and metabolic activity may be low. Specificity of FAPI 04 PET/CT was also higher (95%) compared to FDG PET/CT (88%), reflecting the lower background activity in non-tumor tissues. Lesion detection rates were significantly improved with FAPI 04 PET/CT, with 112 out of 115 lesions identified, while FDG PET/CT detected 98 lesions (p = 0.02). The accuracy of FAPI 04 PET/CT was 94%, whereas FDG PET/CT had an accuracy of 86%. Notably, FAPI 04 PET/CT showed a higher diagnostic yield in detecting metastases in liver, peritoneum, and lymph nodes compared to FDG PET/CT. The average scan time for FAPI 04 PET/CT was 30 minutes, significantly shorter than FDG PET/CT (1 hour 15 minutes). Conclusions: FAPI 04 PET/CT outperforms FDG PET/CT in terms of sensitivity, specificity, and diagnostic accuracy for staging gastrointestinal tumours, particularly in cases with abundant stromal involvement. The reduced background activity and higher lesion detection rate enhance the utility of FAPI 04 PET/CT in clinical practice. Additionally, the walk-in basis for FAPI 04 PET/CT with shorter fasting and scan time offers significant improvements in patient comfort and convenience. Given these advantages, FAPI 04 PET/CT represents a promising alternative to FDG PET/CT for staging GI cancers, with potential implications for improved treatment planning and monitoring.