68Ga-FAPI PET in detection of 18F-FDG PET Negative Cholangiocarcinoma: A Case Report on Alternative Molecular Imaging in Biliary Tract Malignancy

Fibroblast activation protein inhibitors (FAPI) PET is a new imaging approach that targets the cell population in the tumoursurrounding stroma, particularly cancer-associated fibroblasts, rather than tumour cells. 68Ga-FAPI PET/CT FAPI PET/CTprovides better lesion characterisation due to a higher tumour-to-background ratio and exhibits high diagnostic accuracy,especially for cancers that exhibit low-to-moderate uptake of 18F-FDG. We report the case of a 77-year-old woman withknown renal cell carcinoma treated ten years ago, and recently presented with cholangitis and a liver lesion. 18FDG PET-CTshowed a mild hypermetabolic lesion at segment V. 68Ga-FAPI PET/CT was performed for further assessment. 68Ga-FAPIPET/CT demonstrates an intensely tracer avid lesion at hepatic segment V. These findings are likely due to primarycholangiocarcinoma. Biopsy confirms intrahepatic cholangiocarcinoma. 68Ga-FAPI PET/CT FAPI PET/CT provides better lesioncharacterization due to a higher tumor-to-background ratio and exhibits high diagnostic accuracy in cholangiocarcinoma. Keywords: 68Ga-FAPI PET/CT; Cholangiocarcinoma; Fibroblast activation protein; cancer-associated fibroblasts Biliary TractMalignancy.