Utility of 18FDG-PET for differentiating the grade of malignancy in thymic epithelial tumors.

PURPOSE: The objective of this study was to assess the value of (18)F-FDG PET in thymic epithelial tumors according to the WHO histologic classification and to evaluate its potential for differentiating the grade of malignancy in thymic epithelial tumors.

MATERIALS AND METHODS: Thirty-six patients with a thymic epithelial tumor who underwent (18)F-FDG PET examination before treatment were enrolled in the present study. The T/M ratio, which is the ratio of the peak standardized uptake value (SUV) of the tumor to the mean SUV of mediastinum, was compared in subgroups of a simplified WHO histological classification; low-risk thymoma (Types A, AB and B1), high-risk thymoma (Types B2 and B3), and thymic carcinoma.

RESULTS: Tumors included 15 low-risk thymomas, 10 high-risk thymomas and 11 thymic carcinomas. Upon visual inspection, all tumors showed (18)F-FDG accumulation and the mean T/M ratio in these three subgroups was 2.64, 4.29 and 8.90, respectively. The differences between the three subgroups were statistically significant (low-risk vs. high-risk: p=0.01, high-risk vs. thymic carcinoma: p=0.01).

CONCLUSION: A significant relationship was seen between (18)F-FDG PET accumulation and histologic subtype in thymic epithelial tumors when they were classified into three groups. PET may be useful for predicting the grade of malignancy in thymic epithelial tumors.