Comparison of PET imaging of activated fibroblasts and ¹⁸F-FDG for diagnosis of primary hepatic tumours: a prospective pilot study.

Abstract

This study aimed to compare the performance of ⁶⁸Ga-labelled fibroblast activating protein inhibitor (FAPI) PET and ¹⁸F-FDG PET for imaging of hepatic tumours. We prospectively assessed 20 patients with suspected intrahepatic lesions. Tumour radiological features, pathology, or follow-up examinations were assessed as ground truth in correlation with PET scans. Semiquantitative analysis was additionally performed by measuring the standardised uptake value (SUV). Tumour-to-liver background ratios (TBR) were calculated and compared between ⁶⁸Ga-FAPI PET and ¹⁸F-FDG PET. FAPI expression was assessed by immunochemistry in samples obtained from 7 patients with hepatocellular carcinomas (HCC)/intrahepatic cholangiocarcinoma (ICC) or granulomas. Primary intrahepatic tumours, including 16 HCC in 14 patients and 4 ICC in 3 patients with extrahepatic metastases, were determined by histology (n = 14) and clinical examinations (n = 3). Based on visual analysis, 17 patients presented elevated ⁶⁸Ga-FAPI uptake (sensitivity: 100%, specificity: 100%), while 7 patients presented ¹⁸F-FDG avid tumours (sensitivity: 58.8%, specificity: 100%). ⁶⁸Ga-FAPI PET/CT identified 17 extrahepatic metastases vs. 13 in ¹⁸F-FDG PET/CT in 2 ICC patients. Three benign liver nodules in three patients showed negligible uptake in dual-PET scans. The SUV_{max_HCC} = 8.47 ± 4.06 and TBR_{max_HCC} = 7.13 ± 5.52, and SUV_{max_ICC} = 14.14 ± 2.20 TBR_{max_ICC} = 26.46 ± 4.94 in ⁶⁸Ga-FAPI-04 PET/CT were significantly higher than the ¹⁸F-FDG uptake presenting SUV_{max_HCC} = 4.86 ± 3.58 and TBR_{max_HCC} = 2.39 ± 2.21, and SUV_{max_ICC} = 9.19 ± 3.60 and TBR_{max_ICC} = 2.39 ± 2.21 (all p values < 0.05). ICC patients showed higher levels of FAPI uptake in the primary hepatic lesions compared to extrahepatic metastases, TBR_{max_ICC} = 15.18 ± 5.80 (p = 0.04). ⁶⁸Ga-FAPI PET-CT has superior potential in the detection of primary hepatic malignancy compared to ¹⁸F-FDG.