Non-specific uptake of 18F-FAPI-04 in the pancreas and its related factors: a post-hoc analysis of an ongoing prospective clinical trial

Abstract

This study aimed to analyze the characteristics of the non-specific uptake (NSU) of ¹⁸F-labeled fibroblast activation protein inhibitor (¹⁸F-FAPI) of the pancreas and investigate the related factors. Totally, 78 patients who underwent both ¹⁸F-fluorodeoxyglucose (FDG) and ¹⁸F-FAPI PET/CT examinations were divided into normal (n = 53) and NSU (n = 25) groups. The differences in general information, medical history, laboratory indexes and uptake were compared. Receiver operating characteristic (ROC) curves were used to analyze the optimal cut-off values. The correlations between ¹⁸F-FAPI-SUVmax and blood cell analysis, liver function indexes, tumor markers, and inflammatory indices were analyzed. The logistic regression model was used to estimate the independent factors. Both ¹⁸F-FAPI (4.48 ± 0.98 vs. 2.01 ± 0.53, t = 11.718, P < 0.05) and ¹⁸F-FDG (2.23 ± 0.42 vs. 2.02 ± 0.44, t = 2.036, P = 0.045) showed significantly higher in NSU group. Patients in the NSU group tended to be complicated with a history of drinking (P = 0.034), chronic liver diseases (P = 0.006), and surgery of gastrectomy (P = 0.004). ROC analysis showed cutoff values of 3.25 and 2.05 for ¹⁸F-FAPI and ¹⁸F-FDG in identifying the NSU. Patients in the NSU group showed less platelet count, higher platelet volume, higher total bilirubin, direct or indirect bilirubin (P < 0.05). Platelet count, platelet crit, large platelet ratio, aspartate aminotransferase (AST), α-L-fucosidase, and total, direct or indirect bilirubin were correlated with ¹⁸F-FAPI-SUVmax (P < 0.05). AST [1.099 (1.014, 1.192), P = 0.021] and total bilirubin [1.137 (1.035, 1.249), P = 0.007] were two independent factors in the step forward logistic regression, and platelet/% [1.079 (1.004, 1.160), P = 0.039] and total bilirubin [1.459 (1.016, 2.095), P = 0.041] were two independent factors in the step backward logistic regression for the prediction of pancreatic uptake of ¹⁸F-FAPI. ¹⁸F-FAPI-PET/CT was better than ¹⁸F-FDG in predicting the pancreatic NSU, and NSU is related to a history of drinking, chronic liver diseases, gastrectomy, heteromorphic platelet, and impaired liver function.

Keywords: 18F-FAPI; 18F-FDG; Non-specific uptake; pancreas; PET/CT.