Too early to be different? A multi-institutional study with 30-year follow-up for prognostic factors of completely resected early stage thymoma

Background/Purpose: This multi-institutional study was aimed to analyze prognostic factors of completely resected early stage thymoma. Methods: Patients with surgically treated early stage thymoma between 1988 and 2019 were enrolled. Statistical associations were evaluated using the χ² test, Fisher's exact test, and Student's t-test. Disease-free survival (DFS) and overall survival (OS) curves were established by the Kaplan-Meier method, and compared using the log-rank test. Results: A total of 229 patients with Masaoka stage I and 131 with Masaoka stage II thymoma were included. The DFS of patients with Masaoka stage I thymoma was associated with neutrophil-to-lymphocyte ratio (NLR, hazard ratio [HR] = 3.18, 95% confidence interval [CI]: 1.34–7.54), and extrathymic malignancies (HR = 4.51, 95% CI: 2.02–10.11), and the OS was associated with NLR (HR = 5.03, 95% CI: 1.61–15.66) and extrathymic malignancies (HR = 7.68, 95% CI: 3.12–18.97). In patients with Masaoka stage II thymoma, DFS was associated with age (HR = 2.50, 95% CI: 1.18–5.27), extent of surgery (HR = 0.41, 95% CI: 0.19–0.87), and NLR (HR = 3.23, 95% CI: 1.11–9.44), and OS was associated with age (HR = 5.77, 95% CI: 1.81–18.34), surgical approach (HR = 8.40, 95% CI: 1.91–37.00), and extrathymic malignancies (HR = 2.96, 95% CI: 1.08–8.12). Conclusion: In Masaoka stage I thymoma, preoperative NLR and extrathymic malignancies are independently associated with DFS and OS. In Masaoka stage II thymoma, age, extent of surgery, and NLR are independently associated with DFS, and age, surgical approach, and extrathymic malignancies are associated with OS.