To assess the value of ¹⁸F-FDG PET/CT imaging in the differential WHO classification of thymic epithelial neoplasms.

From February 1, 2011 to June 30, 2018, 48 patients with pre-therapy thymic epithelial neoplasms confirmed by surgery or biopsy at Peking University Cancer Hospital were included and divided into three groups: low-risk thymomas, high-risk thymomas, and thymic carcinomas. Bivariate correlation analysis, Student's t test, and ROC curve analysis were used to analyze and compare the clinicopathologic features, features of CT imaging, and FDG metabolism parameters among the three groups of thymic epithelial neoplasms.

Of 48 cases of thymic epithelial neoplasms, 17 were low-risk thymomas, 8 were high-risk thymomas, 23 were thymic carcinomas, 12 had lymph node metastasis, 4 had pleural metastasis, 3 had pulmonary metastasis, and 2 had liver/pericardium/bone metastasis. Tumor capsule (r=0.921, P<0.001), mediastinal invasion (r=0.452, P=0.001), neighboring structure invasion (r=0.865, P<0.001), lymph node metastasis (r=0.505, P<0.001), distant organ metastasis (r=0.383, P=0.008), SUVmax (t=0.626, P<0.001), and SUVmax/maximum tumor diameter ratio (t=0.645, P<0.001) were significantly different among the three groups (P<0.01). Neighboring structure invasion, SUVmax/maximum tumor diameter ratio, and SUVmax were found to be most useful predictive factors to distinguish low-risk thymomas from high-risk thymomas or thymic carcinomas (areas under the ROC curves were 0.952, 0.916, and 0.865, respectively).

¹⁸F-FDG PET/CT can be used to identify different WHO classifications of thymic epithelial neoplasms, and can effectively distinguish low-risk thymomas from high-risk group thymomas or thymic carcinomas.