18F-FAPI-42 PET/CT enhances the diagnostic efficacy for peritoneal metastasis of colorectal cancer and guides treatment decisions: an original retrospective study.

Abstract

Background: Colorectal cancer is the third-most common type of cancer. When peritoneal metastasis (PM) develops, diagnosing metastatic lesions is difficult and the prognosis is poor. This study aimed to compare the value of fluorine-18 fibroblast activation protein-specific inhibitor (¹⁸F-FAPI-42) and fluorine-18 fluorodeoxyglucose (¹⁸F-FDG) positron emission tomography/computed tomography (PET/CT) for detecting PM of colorectal cancer and to guide clinical decision-making.

Methods: Forty-eight patients with PM who underwent both ¹⁸F-FAPI-42 and ¹⁸F-FDG PET/CT examinations were studied. The maximum standardized uptake value (SUV max), tumor-to-background ratios (TBRs) and peritoneal cancer index (PCI) of the PM were compared between the two imaging techniques. The intraclass correlation coefficient (ICC) was used to compare the consistency between the PET/CT PCI score and the intraoperative PCI. A receiver-operating characteristic curve was used to predict the accuracy of CC-0 cytoreduction (complete cytoreduction with no visible disease).

Results: The sensitivity and accuracy of ¹⁸F-FAPI-42 PET/CT for detecting PM were higher than those of ¹⁸F-FDG PET/CT (82.1% vs 61.1%, P < 0.01; 84.6% vs 74.5%, P < 0.01). The median SUV max and TBR of PM was greater in ¹⁸F-FAPI-42 than in ¹⁸F-FDG PET/CT [4.8 (1.9-20.1) vs 4.7 (1.0-11.0), P = 0.02; 4.3 (1.4-14.6) vs 2.9 (0.6-8.0), P < 0.01, respectively]. The median PCI of PM based on ¹⁸F-FAPI-42 PET/CT was greater than that based on ¹⁸F-FDG PET/CT (15 vs 9, P < 0.01). The ICC for ¹⁸F-FAPI-42 PCI was greater than that for ¹⁸F-FDG PCI (0.915 vs 0.724, P < 0.01). The cut-off values of the PCI of the PM for ¹⁸F-FAPI-42 and ¹⁸F-FDG PET/CT to predict CC-0 were <18 and <10, with areas under the curve of 0.80 and 0.79, respectively.

Conclusions: ¹⁸F-FAPI-42 PET/CT has superior diagnostic efficacy for PM, particularly in the right upper epigastrium and small intestine. The PCI score of ¹⁸F-FAPI-42 PET/CT is very close to the intraoperative PCI score and has a high value for predicting CC-0. The individualized management of PM based on the ¹⁸F-FAPI-42 PET/CT PCI score is pivotal.