18F-fluorodeoxyglucose and 11C-acetate positron emission tomography are useful modalities for diagnosing the histologic type of thymoma.

Abstract

The objective of this study was to clarify the usefulness of positron emission tomography (PET) using(18)F-fluorodeoxyglucose (FDG) and carbon 11-labeled acetate (AC) for predicting the histologic types and tumor invasiveness of thymoma in a multicenter study. 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 B1 in 11 thymomas, type B2 in 7 thymomas, type B3 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 II 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). 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 >or=6.3, and all 13 type A/AB tumors had an FDG-SUV <6.3 and an AC-SUV >or=5.7. All 17 thymomas that had an FDG-SUV <6.3 and an AC-SUV <5.7 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. 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 >or=5.7 almost certainly are types A/AB, which is of considerable prognostic and management significance.