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18F-Fluorodeoxyglucose Positron Emission Tomography in the Management of Patients with Thymic Epithelial Tumors

Purpose: There are limited data regarding the role of 18F-fluorodeoxyglucose positron emission tomography ([18F]-FDG PET) imaging in management of patients with thymic epithelial tumors (TET). The primary objective of this study was to assess the usefulness of early [18F]-FDG PET to monitor treatment efficacy and its correlation with Response Evaluation Criteria in Solid Tumors (RECIST) in patients with TETs. Experimental Design: [18F]-FDG PET/computed tomographic (CT) scans were conducted at baseline and after 6 weeks of treatment in patients enrolled in two phase II and one phase I/II clinical trials. On the basis of data from other solid tumors, metabolic response was defined as a reduction of [18F]-FDG uptake by more than 30% as assessed by average standardized uptake values (SUV) of up to five most metabolically active lesions. Results: Fifty-six patients with unresectable Masaoka stage III or IV TETs were included. There was a close correlation between early metabolic response and subsequent best response using RECIST (P < 0.0001–0.0003): sensitivity and specificity for prediction of best response were 95% and 100%, respectively. Metabolic responders had significantly longer progression-free survival (median, 11.5 vs. 4.6 months; P = 0.044) and a trend toward longer overall survival (median, 31.8 vs. 18.4 months; P = 0.14) than nonresponders. [18F]-FDG uptake was significantly higher in thymic carcinoma than in thymoma (P = 0.0004–0.0010). Conclusion: In patients with advanced TETs, early metabolic response closely correlates with outcome of therapy. [18F]-FDG PET may be used to monitor treatment efficacy and assess histologic differences in patients with advanced TETs. Clin Cancer Res; 19(6); 1487–93. ©2013 AACR.