Real-world evidence in a large cohort comparing FAPI and FDG PET/CT for hepatopancreatobiliary cancer diagnosis

Diagnosing hepatopancreatobiliary (HPB) malignancies remains challenging. Conventional imaging often lacks sensitivity for occult nodal and distant metastases, and FDG PET/CT has variable performance due to low uptake in several tumour subtypes and false-positive uptake in inflammation. Fibroblast activation protein inhibitor (FAPI) PET/CT has emerged as a promising alternative. This study compared the diagnostic accuracy of FDG PET/CT, FAPI PET/CT, and a dual-tracer approach in suspected HPB malignancies.

This retrospective analysis included patients who underwent both [¹⁸F]FDG and [⁶⁸Ga]Ga-FAPI-46 PET/CT for suspected HPB cancer, including cholangiocarcinoma, gallbladder carcinoma, pancreatic carcinoma, periampullary carcinoma, and hepatocellular carcinoma. Histopathology and/or clinical follow-up served as reference standard. FDG PET/CT classification used an SUV_max cut-off derived from receiver-operating characteristic analysis, while FAPI PET/CT classification followed expert clinical interpretation. Sensitivity, specificity, and accuracy metrics were compared using paired statistics.

176 patients were included. FAPI PET/CT demonstrated higher sensitivity than FDG PET/CT (93.0% vs. 76.5%, p = 0.002). Primary tumour diagnostic accuracy was 78.9% for FAPI versus 68.3% for FDG (p = 0.021). A dual-tracer approach did not outperform FAPI (76.7% vs. 78.9%, p = 0.711). For nodal disease, FAPI showed 86.8% diagnostic accuracy, compared with 71.1% for FDG (p = 0.004), driven by higher specificity. For distant metastases, accuracy was 83.9% for FAPI versus 80.0% for FDG (p = 0.625).

FAPI PET/CT outperformed FDG PET/CT in this retrospective analysis, with dual-tracer imaging offering no additional benefits. These results show great promise for clinical application of FAPI PET/CT for the detection of HPB tumours and their metastases to be confirmed by independent prospective studies.