Prognostic value as metabolic tumor activity on ¹⁸F-FDG uptake in thymic epithelial tumors

Thymic epithelial tumors (TETs) are rare neoplasms; however, optimal predictors after initial treatment are unclear. ¹⁸F-fluorodeoxyglucose positron emission tomography (¹⁸F-FDG PET) is useful for differentiating malignant from benign lesions and has the potential to serve as a prognostic predictor. This retrospective study investigated the prognostic significance of ¹⁸F-FDG PET in patients with TETs.

A total of 108 consecutive patients with TETs classified as thymoma or thymic carcinoma (TC) who received ¹⁸F-FDG PET before any treatment between August 2007 and March 2020 were eligible for this study. For ¹⁸F-FDG uptake, the maximum standardized uptake value (SUVmax), metabolic tumor volume (MTV), and total lesion glycolysis (TLG) were assessed for prognostic prediction.

Univariate analysis identified performance status (PS), smoking, disease stage, histology, SUVmax, MTV, and TLG as significant predictors of progression-free survival (PFS) and overall survival (OS). In the multivariate analysis, TLG was an independent prognostic factor for predicting worse PFS, and histology emerged as a significant predictor for OS. In patients with thymoma, univariate analysis identified disease stage, SUVmax, MTV, and TLG as significant predictors for PFS but not OS. In patients with TC, univariate analysis identified PS, disease stage, smoking status, SUVmax, MTV, and TLG as significant predictors for both PFS and OS.

Indicators of ¹⁸F-FDG uptake, including SUVmax, MTV, and TLG, can predict poor outcomes in patients with TETs. Increased accumulation of ¹⁸F-FDG was closely associated with poor PFS in specific populations, such as those with thymoma or TC, but not OS.