AB030. Clinical significance of SUVmax as a predictor of pathological invasion and prognostic factor in advanced thymic epithelial tumors requiring a combined resection of adjacent organs and dissemination

Background: Thymic epithelial tumors (TETs) are rare and heterogeneous malignancies. Because they are surrounded by vital mediastinal structures, achieving complete (R0) resection and determining the extent of lymph node dissection are often challenging in advanced cases. Therefore, accurate preoperative assessment of tumor invasiveness is of critical importance for treatment planning. The maximum standardized uptake value (SUVmax) has been reported to correlate with biological aggressiveness and tumor progression in various malignancies. However, its clinical significance in TETs remains insufficiently clarified, and the association with tumor size has also been scarcely investigated. This study aimed to evaluate the clinical utility of SUVmax as a predictor of pathological invasion and a prognostic factor in advanced TETs requiring combined resection of adjacent organs or management of dissemination. Methods: A multicenter retrospective study was conducted, comprising 102 patients with TETs, requiring combined resections of adjacent organs or pleural disseminations, from January 2000 to November 2024. Among these, 53 patients with available SUVmax data were included. Receiver operating characteristic (ROC) curves were used to determine optimal SUVmax and tumor size cut-offs for predicting advanced pathological stage (Masaoka stage III/IV) and nodal metastasis. Logistic regression identified factors associated with pathological invasion. Progression-free survival (PFS) was analyzed using Kaplan-Meier methods (log-rank test) and Cox hazard model. Results: Twenty-five thymomas and 27 thymic carcinomas or thymic neuroendocrine tumors were analyzed. The median SUVmax and tumor size were 5.3 [interquartile range (IQR), 3.8–8.4] and 5.5 (IQR, 5.5–8.0) cm, respectively. Pathological staging revealed 2 stage I, 9 stage II, 29 stage III, 4 stage IVa, and 9 stage IVb cases. Both SUVmax and tumor size were significant predictors of advanced stage and nodal involvement. ROC analysis identified SUVmax cut-offs of 4.7 for advanced disease [area under the curve (AUC) =0.685, sensitivity 71.4%, specificity 63.6%] and 6.1 for nodal involvement (AUC =0.765, sensitivity 77.8%, specificity 68.2%). Tumor size cut-offs were 5.6 cm for both events. Combination of SUVmax (≥4.7 or ≥6.1) and tumor size (≥5.6 cm) stratified risk: rates of advanced disease were 45.5%, 80.0%, and 100% (P<0.001) and nodal involvement rates were 0%, 15.0%, and 46.2% (P=0.001) for patients with 0, 1, and 2 risk factors, respectively. During a median follow-up of 34 months, 15 disease progressions/relapses were observed. High SUVmax (≥6.1) was associated with significantly worse PFS compared to low SUVmax (<6.1) (P<0.001; 5-year PFS, 41.9% vs. 77.5%; hazard ratio 4.53, 95% confidence interval: 1.53–13.4). No significant interactions were found between SUVmax and tumor size, stage, or histology. Conclusions: SUVmax is a valuable indicator of pathological invasion along with tumor size and may guide surgical decision-making and nodal dissection strategy. Furthermore, SUVmax serves as a prognostic factor in advanced TETs.