The Desmoid Tumor Research Foundation

January 2026

Differential [18F]FAPI-42 and [18F]FDG uptake patterns distinguish desmoid tumours from GISTs on PET/CT imaging

Author Information

Chunhui Wu # 1 2, Xiaoyan Wang # 1, Xiaojie Lin 1, Andor W J M Glaudemans 2, Bart Cornelissen 2, Walter Noordzij 2, Xin Hu 1, Yu Zeng 1, Xiangsong Zhang 3, Xinhua Zhang 4

1Department of Nuclear Medicine, The First Affiliated Hospital of Sun Yat-sen University, 58 2nd Zhongshan Road, Guangzhou, Guangdong Province, 510080, China. 2Department of Nuclear Medicine and Molecular Imaging, University of Groningen, University Medical Center Groningen, Groningen, the Netherlands. 3Department of Nuclear Medicine, The First Affiliated Hospital of Sun Yat-sen University, 58 2nd Zhongshan Road, Guangzhou, Guangdong Province, 510080, China. zhxiangs@mail.sysu.edu.cn. 4Center for Gastrointestinal Surgery, The First Affiliated Hospital of Sun Yat-sen University, #58, 2nd Zhongshan Road, Guangzhou, Guangdong Province, 510080, China. zhangxinhua@mail.sysu.edu.cn. #Contributed equally.

Publication

Eur J Nucl Med Mol Imaging

Summary

Background: Intra-abdominal desmoid tumours (IADT) can closely mimic gastrointestinal stromal tumours (GISTs), particularly in recurrence and metastases. However, differentiating these two diseases using radiological methods remains challenging. This study aimed to investigate the value of [18F]FAPI-42 PET/CT in differentiating IADT and GISTs compared to [18F]FDG PET/CT. Methods: This study retrospectively included a total of 24 patients (12 patients with IADT and 12 patients with recurrent/metastatic GISTs) who underwent two separate PET/CT scans using [18F]FAPI-42 and [18F]FDG, respectively. The differences in tumour SUVmax on [18F]FAPI-42 PET/CT (SUVmax-FAPI) and [18F]FDG PET/CT (SUVmax-FDG) and the ratio of tumour SUVmax on FAPI PET/CT to SUVmax on FDG PET/CT [SUVmax ratio (FAPI/FDG)] were compared between IADT and GISTs. Receiver operating characteristic (ROC) curve analyses were performed to evaluate the diagnostic performance of these parameters in differentiating IADTs from GISTs. Immunohistochemistry was used to verify FAP expression in all IADT lesions and GISTs lesions. Results: The SUVmax of IADTs on [18F]FAPI-42 PET/CT was significantly higher than that of GISTs [8.8 (7.2, 10.6) vs. 3.9 (2.8, 7.6), P = 0.045], whereas the SUVmax of IADTs on [18F]FDG PET/CT was significantly lower than that of GISTs [2.5 (1.9, 3.5) vs. 6.1 (3.6, 8.3), P = 0.007]. The SUVmax ratio (FAPI/FDG) of IADTs was significantly higher than that of GISTs [3.3 (2.2, 4.1) vs. 0.8 (0.3, 1.4), P < 0.001]. SUVmax-FAPI, SUVmax-FDG, and the SUVmax ratio (FAPI/FDG) achieved AUCs of 0.743, 0.819, and 0.896, with corresponding accuracies of 75.0%, 83.3%, and 87.5%, respectively, for distinguishing IADT from GISTs. Immunohistochemistry revealed significantly higher FAP expression in IADTs compared to GISTs (P = 0.002), with most IADTs showing strong (3+) staining (8/12, 66.7%), while GISTs primarily demonstrated weak (1+) or no staining (7/12, 58.3%). Conclusion: The distinct uptake characteristics of [18F]FAPI-42 and [18F]FDG observed in IADTs and GISTs provide preliminary evidence that these two tracers may offer complementary diagnostic information when evaluating desmoid tumours that mimic recurrent or metastatic GISTs.

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