The Role of [18F]F-FDG PET/CT for Predicting Histology and Prognosis in Patients with Thymic Lesions.

Objectives: To investigate whether 18F-fluorodeoxyglucose positron emission tomography-computed tomography ([¹⁸F]F-FDG PET/CT) metabolic parameters were associated with histology and to assess their prognostic role in patients with thymic lesions.

Patients and methods: In total, 116 patients (49/67 M/F; mean age 59.5 years) who underwent preoperative [¹⁸F]F-FDG PET/CT and thymectomy from 2012 to 2022 were retrospectively analyzed. Associations between histology and metabolic parameters (maximum standardized uptake value (SUVmax), mean standardized uptake value (SUVmean), peak standardized uptake value (SUVpeak), total lesion glycolysis (TLG), metabolic tumor volume (MTV), ratio between target lesion and liver SUVmax (rPET), quotient of SUVpeak in the tumor residual and SUVmean in a 20-cm³ volume of interest (qPET), and tumor-to-mediastinum (T/M) were analyzed. Freedom from recurrence (FFR) was determined and compared using the Kaplan-Meier and the log-rank test. The median follow-up was 38 months (range 14-72 months).

Results: In total, 27 thymic hyperplasia, 41 low-risk thymomas (LRT) (types A, AB, and B1), and 48 high-risk thymomas (HRT) (B2, B3 thymoma, and carcinoma) were included. SUVmax, SUVmean, SUVpeak, rPET, qPET, and T/M were significantly higher in HRT than LRT and hyperplasia (p < 0.001). TLG and MTV were significantly higher in patients with LRT (p < 0.001). Only rPET, qPET, and T/M remained significantly higher in HRT than in LRT subgroups (p = 0.042, p = 0.049, and p = 0.028, respectively). SUVmax, SUVmean, and SUVpeak cutoffs of < 4.3, < 2.87, and 4.03, respectively, significantly distinguished patients with longer FFR (p = 0.009, p = 0.05, and p = 0.05).

Conclusions: Positron emission tomography (PET) metabolic parameters could help to differentiate thymic histotypes. Standardized uptake value (SUV)-based parameters appear promising to predict recurrent disease.