F-18-Fluorodeoxyglucose and C-11-Acetate Positron Emission Tomography Are Useful Modalities for Diagnosing the Histologic Type of Thymoma

BACKGROUND: The objective of this study was to clarify the usefulness of positron emission tomography (PET) using F-18-fluorodeoxyglucose (FDG) and carbon 11-labeled acetate (AC) for predicting the histologic types and tumor invasiveness of thymoma in a multicenter study. METHODS: Forty thymomas were examined using both FDG-PET and AC-PET before surgery. The histologic types were type A in 1 thymoma, type AB in 12 thymomas, type 131 in 11 thymomas, type B2 in 7 thymomas, type 133 in 6 thymomas, and type C in 3 thymomas. Tumor invasiveness was assessed by pathologic tumor stage and was identified as stage I in 17 tumors, stage 11 in 17 tumors, stage III in 4 tumors, and stage IV in 2 tumors. FDG and AC uptake was measured as the maximum standard uptake value (SUV). RESULTS: The FDG-SUV in type C thymomas was significantly higher than that in the other types (A-B3; P=.001 - P=.048). The AC-SUV in type A/AB thymomas was significantly higher than that in the other tumor types (B1-C; P<.001 - P=.002). All 3 type C tumors had an FDG-SUV >= 6.3, and all 13 type A/AB tumors had an FDG-SUV <6.3 and an AC-SUV >= 5.7 All 17 thymomas that had an FDG-SUV <6.3 and an AC-SUV <57 were type B1, B2, or B3. Neither the FDG-SUV nor the AC-SUV differed significantly between the stages I/II tumors and stage III/IV tumors. CONCLUSIONS: Although neither the FDG-SUV nor the AC-SUV can predict the invasiveness of thymomas assessed by tumor stage, they are useful for predicting histologic types of thymoma. Thymomas with an FDG-SUV <6.3 and an AC-SUV >= 5.7 almost certainly are types A/AB, which is of considerable prognostic and management significance. Cancer 2009; 115:2531-8. (C) 2009 American Cancer Society.