UTILITY OF 18F-FLUORODEOXYGLUCOSE POSITRON EMISSION TOMOGRAPHY FOR DISTINGUISHING BETWEEN THE HISTOLOGIC TYPES OF EARLY STAGE THYMIC EPITHELIAL TUMORS

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Abstract

Objectives

Recent studies have shown the usefulness of 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) in differentiatingbetween World Health Organization (WHO) histological subgroups of thymic epithelial tumours. However, these reports may have includedmany advanced cases of these lesions (Masaoka stage III or IV) of high-risk subtypes. The objective of our present study was to assess the usefulnessof FDG-PET for distinguishing the histological subtypes of early stage thymic epithelial tumours (Masaoka stage I or II).

Methods

Twenty patients who had undergone an FDG-PET examination before treatment and had been diagnosed with an earlystage thymic epithelial tumour between July 2005 and July 2011 were enrolled in the present study. All patients underwent a total thymectomy.This cohort was divided into two groups according to the WHO histological classification of their lesion, i.e. low-risk tumours (types A, AB or B1) in one group and high-risk tumours (types B2, B3 or thymic carcinoma) in the other. Focal FDG accumulation was evaluated by determining the maximum standardized uptake value (SUV-max).

Results

The patient cohort for this study included 13 men and 7 women ranging in age from 26 to 70 years (mean 55 years). The low-risk group included seven cases (type A, 0; type AB, 7; type B1, 0), and the high-risk group comprised 13 cases (type B2, 7; type B3, 3; thymic carcinoma, 3). The SUV-max values of the low- and high-risk tumours were 3.09 ± 0.51 and 6.19 ± 3.13, respectively, and this was a significant difference. For the differential diagnosis of low- and high-risk tumours, sensitivity and specificity were 92.3 and 83.3%, respectively, when an SUV-max of 3.5 was used as a cutoff.

Conclusions

FDG-PET is a useful method for distinguishing histological types of early-stage thymic epithelial tumours.

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