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Can 18F-FDG PET predict the grade of malignancy in thymic epithelial tumors? An evaluation of only resected tumors

Authors Nakagawa K, Takahashi S, Endo M, Ohde Y, Kurihara H, Terauchi T

Received 15 July 2017

Accepted for publication 3 October 2017

Published 5 December 2017 Volume 2017:9 Pages 761—768


Checked for plagiarism Yes

Review by Single-blind

Peer reviewer comments 2

Editor who approved publication: Professor Nakshatri

Kazuo Nakagawa,1 Shoji Takahashi,2 Masahiro Endo,3 Yasuhisa Ohde,2 Hiroaki Kurihara,4 Takashi Terauchi5

1Department of Thoracic Surgery, National Cancer Center Hospital, Tokyo, 2Division of Thoracic Surgery, 3Division of Diagnostic Radiology, Shizuoka Cancer Center, Shizuoka, 4Department of Diagnostic Radiology, National Cancer Center Hospital, 5Department of Nuclear Medicine, Cancer Institute Hospital, Tokyo, Japan

Objective: Although 18-fluorine fluorodeoxyglucose positron emission tomography (18F-FDG PET) is thought to be useful for predicting the histological grade of thymic epithelial tumors (TETs), it remains controversial. To date, just a few of many previous studies have included only resected cases. Therefore, we investigated 18F-FDG PET findings only in patients with resected TETs.
Patients and methods:
A total of 112 patients with TETs consisting of 92 thymomas and 20 thymic carcinomas (TCs), resected at two institutes (Shizuoka Cancer Center [Shizuoka] and National Cancer Center Hospital [Tokyo]) between October 2002 and December 2015, were evaluated. Spearman rank correlation coefficient was used to assess the association between the maximum standardized uptake value (SUVmax) in the tumor and both the histological subtype and tumor stage. The cutoff value of SUVmax for differentiating thymoma from TC was calculated.
Results: The SUVmax was strongly related to both the World Health Organization (WHO) histological subtype and tumor stage based on the eighth edition of the tumor-node-metastasis (TNM) classification (Spearman rank correlation coefficient =0.485 and 0.432; p = 0.000 and 0.000, respectively). There was a significant difference between thymoma and TC. The optimal SUVmax cutoff value for differentiating thymoma from TC was 4.58 (sensitivity: 80% and specificity: 78.3%). In contrast, there was no significant difference between low-risk (type A, AB, and B1) and high-risk (type B2 and B3) thymoma, or between type B3 thymoma and the other subtypes.
Our results suggest that 18F-FDG PET is useful for differentiating thymoma from TC, but not for predicting the histologic grade of thymoma.

Keywords: 18F-FDG PET, thymic epithelial tumors, thymoma, thymic carcinoma, WHO histological subtype, TNM classification

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