18F-fluorodeoxyglucose positron emission tomography-computed tomography as a prognostic marker of imatinib-resistant gastrointestinal stromal tumors

Purpose Unresectable or metastatic GISTs often develop resistance to imatinib, but the effectiveness of other drugs is limited. Thus, surgical treatment can be considered, especially for partial resistance. FDG-PET/CT is used for the diagnosis and evaluation of GISTs. We conducted this study to establish whether FDG-PET/CT findings could guide treatment decisions and predict the prognosis of patients with imatinib-resistant GISTs. Methods We analyzed data retrospectively from 45 patients with imatinib-resistant GISTs that were assessed via FDG-PET/CT at our institution between 2003 and 2021. The patients were classified as having low (n = 18) or high (n = 27) SUVmax, with a cutoff value of 5.0. Results The overall survival (OS) of the patients with low SUVmax after the diagnosis of imatinib resistance was significantly prolonged. Multivariate analysis identified SUVmax as an independent poor prognostic factor. In 23 patients with resected imatinib-resistant lesions, a close correlation was found between the SUVmax by preoperative FDG-PET/CT and the mitotic rate. A higher SUVmax was associated with a higher mitotic rate. Patients with a low SUVmax (n = 11) had significantly longer postoperative imatinib failure-free survival than those with a high SUVmax (n = 12). Conclusions FDG-PET/CT assessment and diagnosis might reveal the pathological grades of imatinib-resistant GISTs and act as a prognostic marker.