Identifying intra-abdominal desmoid type fibromatosis mimicking recurrence/metastasis of GISTs using FAPI PET/CT.

Authors

Chunhui Wu

Published

June 1, 2024

Abstract

e23516 Background: Intra-abdominal desmoid tumor (IADT) can mimic the recurrence/metastases of gastrointestinal stromal tumors (GISTs). However, it is difficult to radiologically differentiate IADT and recurrence/metastases of GISTs. This study aims to investigate the value of 18 F fibroblast activation protein inhibitor ( [ 18 F]FAPI-42) PET/CT in identifying intra-abdominal desmoid type fibromatosis mimicking recurrence/metastases of GISTs by comparing it to [ 18 F]FDG PET/CT. Methods: This study retrospectively included a total of 24 patients (12 patients with IADT and 12 patients with recurrent/metastatic GISTs). The differences in [ 18 F]FAPI-42 PET/CT parameters (SUV max -FAPI and SUV TLR -FAPI ), [ 18 F]FDG PET/CT parameters (SUV max -FDG and SUV TLR -FDG), SUV fapi /SUV fdg ratio of IADT and GISTs were compared. The difference in PET/CT parameters (SUV max , SUV TLR ) of IADT between FDG PET/CT and FAPI PET/CT were compared. Immunohistochemical verification was performed on IADT lesions of all 12 patients and expression profiles of GEO datasets were analyzed to validate the FAP expression of IADT. Results: Both [ 18 F]FAPI-42 PET/CT parameters, SUV max -FAPI [8.8 (2.0, 16.0) vs 1.9 (1.0, 6.0), P< 0.001]and SUV TLR -FAPI [7.3 (2.0, 15.8) vs 1.7 (0.5, 6.9), P< 0.001], of IADT was significantly higher than that of GISTs, while there was no statistically significant difference in [ 18 F]FDG PET/CT parameters, SUV max -FDG and SUV TLR -FDG, between this two group. The ratio (SUV fapi /SUV fdg ) of IADT was significantly higher than that of GISTs [3.3 (1.5, 8.0) vs 0.5 (0.1, 3.9), P= 0.001]. The SUV max and SUV TLR of FAPI PET/CT of IADT were significantly higher than that of FDG PET/CT [8.8 (2.0, 16.0) vs 2.5 (1.1, 6.2), P< 0.001; 7.3 (2.0, 15.8) vs 0.9 (0.4, 2.7), P< 0.001; respectively]. FAP expression was found to be expressed in all the examined tissues and highly expressed in most of them. GEO database analysis shows that the FAP gene expression in DT is significantly higher than that in GISTs. Conclusions: FAPI PET/CT is a promising method in differentiating IADT from recurrence/metastases of GISTs compared with FDG PET/CT since FAP expression in DT is significantly higher than that in GISTs.