Usefulness of 18-F FDG PET/CT in the pre-treatment evaluation of thymic epithelial neoplasms

Background: To assess the usefulness of 18 fluorine-fluorodeoxyglucose positron emission tomogra- phy/computed tomography (18 F-FDG PET/CT) for differentiating the grade of malignancy of thymic epithelial neoplasm, and to determine whether 18 F-FDG PET/CT can have a role in pretreatment evaluation and possibly modify treatment strategy. Materials and methods: The data of 26 consecutive patients (14 males and 12 females) diagnosed with a thymic epithelial neoplasm were prospectively collected and analyzed retrospectively. All patients under- went standard clinical assessment and 18 F-FDG PET/CT. The patients were divided into two subgroups according to a simplified histologic classification: low-risk thymoma (types A, AB and B1) and high-risk thymoma (types B2, B3 and C). The maximum standardized uptake value (SUV max ) of the tumor, the mean SUV of mediastinum, and the tumor/mediastinum (T/M) ratio (ratio of peak SUV of the tumor to mean SUV of mediastinum) were compared to determine whether the two subgroups (low-risk versus high-risk tumors) could be distinguished by 18 F-FDG PET/CT, and to test for possible correlations between 18 F-FDG uptake and disease stage. Results: There was a strong statistical correlation between SUV max and patient subgroup and between SUV max and disease stage, and an even stronger correlation between SUV max and patient subgroup and the T/M ratio; a T/M ratio of 2.75 emerged as the cut-off value for differentiating between low-risk and high-risk thymomas. Conclusions: 18 F-FDG PET/CT can be used a “metabolic biopsy” to divide thymic epithelial neoplasm into two subgroups of high and low risk and is useful in pretreatment staging.