Role of 18F-FDG PET in selecting minimally invasive surgery candidates for thymic epithelial tumor resections

Purpose: We evaluated the potential of preoperative fluorine-18-fluorodeoxyglucose positron emission tomography (18F-FDG PET) to predict invasive thymic epithelial tumors (TETs) in patients with computed tomography (CT)-defined clinical stage I TETs ≤ 5 cm in size who are generally considered to be candidates for minimally invasive approaches (MIAs).

Methods: From January 2012 to April 2022, we analyzed retrospectively 157 patients with resected TETs which were assessed preoperatively by 18F-FDG PET. Among these, 100 exhibited clinical stage I TETs (thymoma, 84; thymic carcinoma, 14; carcinoid, 2) with lesion sizes ≤ 5 cm (as determined by CT imaging) (MIA-candidate cases). We analyzed the association of maximum standardized uptake values (SUVmax) with the World Health Organization histological classification and tumor-node-metastasis (TNM) staging classification. The cut-off values of SUVmax were determined by using a receiver operating characteristic curve analysis.

Results: There were seven patients (7%) who were pathologically upstaged: TNM stage II in two (2%), III in three (3%), and IV in two patients (2%). Two patients with pathological stage II had type B2 or B3 thymomas, while all five patients with stage III/IV had thymic carcinomas. The SUVmax was a predictive factor that distinguished thymic carcinomas from other thymic tumors (best cut-off value, 4.5; AUC = 0.882, 95% confidence interval, 0.740–0.951; sensitivity, 85.7%; specificity, 70.6%). There was no significant difference in SUVmax between stages I and II (P = 0.776), while SUVmax values were significantly higher in stages III/IV compared with those in stages I/II (P < 0.001). Using the cut-off value for thymic carcinoma, the sensitivity and specificity rates for stage III/IV prediction were 100% and 79.9%, respectively.

Conclusion: 18F-FDG PET can be helpful in predicting thymic carcinoma and invasive TETs even in MIA-candidate TET cases. Low-FDG uptake TETs are good candidates for MIA; however, thoracic surgeons should determine carefully the surgical approach for high-FDG uptake TETs and keep in mind the issues associated with potential combined resections of neighboring structures.

Identify the source of the funding for this research project: None