¹⁸F-fluorodeoxyglucose positron emission tomography for evaluation of thymic epithelial tumors: utility for World Health Organization classification and predicting recurrence-free survival

¹⁸F-fluorodeoxyglucose positron emission tomography (FDG-PET) plays an important role in many oncological settings. In this study, we assessed the utility of ¹⁸F-FDG-PET for predicting the histological classification, stage and survival of thymic epithelial tumors.

We retrospectively analyzed 37 patients with thymic epithelial tumors who underwent PET before surgical resection and investigated the relationship between the maximum of standardized uptake value (SUVmax) of each tumor and the WHO classification, recurrence-free survival, and tumor-related gene expressions.

The study included 15 males and 22 females, ranging in age from 22 to 81 years (mean 64 years). The tumor histology of 31 tumors was thymoma and that of the remaining tumors was thymic carcinoma. The Masaoka tumor stage was as follows: stage I in 18, II in 9, III in 5 and IV in 5 patients. The patients were divided into three groups according to a simplified histologic classification: low-risk thymoma (types A, AB and B1, n = 21), high-risk thymoma (types B2 and B3, n = 10) and thymic carcinoma (n = 6). The SUVmax of low-risk group (SUVmax ≤4.27) was significantly lower than that of high-risk group (p = 0.0114) and that of thymic carcinomas (SUVmax >4.27) was also significantly higher than that of thymomas (p < 0.0001). The group of high SUVmax (SUVmax >4.27) had significantly inferior recurrence-free survival to that of less value (SUVmax ≤4.27) (p = 0.0009). The SUVmax were not correlated with tumor-related gene expressions.

The SUVmax of ¹⁸F-FDG-PET reflects WHO classification of thymic epithelial tumors. High SUVmax predicts lower recurrence-free survival of the tumors.