Evaluation of metabolic response with 18F-FDG PET-CT in patients with advanced or recurrent thymic epithelial tumors

BACKGROUND: Patients with advanced or recurrent thymic epithelial tumors (TETs) often need several consecutive lines of chemotherapy. The aim of this retrospective monocentric study was to test whether 18F-Fluorodeoxyglucose positron emission tomography-computed tomography (18F-FDG PET-CT) is able to monitor standard chemotherapy efficacy in those patients and whether metabolic response correlates with morphovolumetric response as assessed by Response Evaluation Criteria in Solid Tumor (RECIST). METHODS: We evaluated 27 consecutive patients with advanced (16 patients) or recurrent (11 patients) TETs. All patients underwent 18F-FDG PET-CT before and after at least 3 cycles of chemotherapy. Maximum standardized uptake value (SUVmax) of all detected lesions was recorded and the most 18F-FDG avid lesion in each patient was selected for determination of percentage change of SUVmax (ΔSUVmax) in pre- and post-treatment scans. Tumor response was assessed by contrast-enhanced computed tomography (CE-CT) using RECIST criteria. Receiver operating characteristic (ROC) curve analysis was performed to define the optimal threshold of ΔSUVmax discriminating responders from non-responders. RESULTS: Metabolic response expressed as ΔSUVmax was significantly correlated with morphovolumetric response (Spearman's rank correlation, r = 0.64, p = 0.001). ROC curve analysis showed that a ΔSUVmax value of -25% could discriminate responders from non-responders with a sensitivity of 88% and a specificity of 80%. Conversely, basal SUVmax values were not predictive of morphovolumetric tumor response. CONCLUSIONS: Our findings indicate that metabolic response assessed by 18F-FDG PET-CT, through evaluation of ΔSUVmax, may allow identification of responders and non-responders thus guiding adaptation of therapy in patients with advanced or recurrent TETs.