The goal of this prospective observational study is to evaluate whether Gallium-68 Fibroblast Activation Protein Inhibitor (FAPI) PET/CT can improve detection, staging, and recurrence assessment in adult patients (≥18 years) with suspected or confirmed biliary tract cancers, including gallbladder cancer, cholangiocarcinoma, and post-treatment suspected recurrence.

The main question(s) this study aims to answer are:

Can FAPI PET/CT provide greater sensitivity, specificity and diagnostic accuracy for primary tumors, nodal disease, and metastatic lesions compared to standard FDG PET/CT?

Does FAPI PET/CT offer additional diagnostic yield that may affect clinical decision-making and staging, potentially reducing need for invasive staging procedures?

Researchers will compare FAPI PET/CT with FDG PET/CT to see if FAPI improves detection of metastatic or recurrent disease, especially peritoneal or liver metastasis and lymph node involvement.

Participants will:

Provide written informed consent.

Undergo FAPI PET/CT imaging (baseline and/or at suspected biochemical or radiologic recurrence).

Have quantitative imaging parameters evaluated (SUVmax, tumor-to-liver ratios, metabolic volume).

May undergo comparison with FDG PET/CT and/or follow-up imaging or histopathology as gold standard.

Biliary tract cancers frequently present at an advanced stage and require accurate staging to guide treatment decisions such as surgery, systemic therapy, or palliative management. Although 18 F-FDG PET/CT is widely used in clinical practice, its diagnostic performance is limited in detecting small primary lesions, nodal metastasis, liver metastasis, and peritoneal carcinomatosis. Gallium-68 Fibroblast Activation Protein Inhibitor (FAPI) PET/CT is a novel imaging technology that targets cancer-associated fibroblasts, which are abundant in the desmoplastic stroma characteristic of biliary tract cancers. Early evidence suggests that FAPI PET/CT may provide improved lesion detectability and tumor-to-background contrast compared to FDG PET/CT.

This prospective observational study will evaluate the clinical utility of Ga-68 FAPI PET/CT for initial staging and suspected recurrence in patients with biliary tract cancers. Diagnostic performance metrics (sensitivity, specificity, PPV, NPV, and semi-quantitative PET parameters such as SUVmax and metabolic volume) will be assessed and compared with FDG PET/CT and/or follow-up imaging or histopathology as the gold standard. The study aims to determine the incremental diagnostic contribution of FAPI PET/CT and its potential impact on clinical decision-making.

Findings from this research may help define the role of FAPI PET/CT as a complementary or alternative imaging modality in staging and restaging of biliary tract cancers and may support future prospective multicenter trials.

Inclusion Criteria:

• Suspected biliary tract cancers- iHCC and GBC
• Male and females ≥ 18 years;
• Upfront advanced (suspected T3 ,T4, N1, vascular involvement)
• iGBC (residual, N1)
• Suspected post-treatment recurrence (biochemical or radiological)

Exclusion Criteria:

• Informed consent withdrawal
• Concurrent Malignancy

The study population will include adult male and female patients (≥18 years) with suspected or confirmed biliary tract cancers, including intrahepatic cholangiocarcinoma (iHCC) and gallbladder cancer (GBC). Eligible participants include individuals with upfront advanced disease (suspected T3/T4 tumors, N1 nodal involvement, or vascular involvement), patients with residual or node-positive incidental gallbladder cancer (iGBC), and those with suspected post-treatment recurrence based on biochemical markers or radiologic evaluation.