Tumor size as a prognostic factor in limited-stage thymic epithelial tumors: A multicenter analysis

Objective: The prognostic significance of tumor size in thymic epithelial tumors (TETs) has not been fully evaluated. We aimed to clarify the prognostic value of tumor size in limited-stage and advanced-stage TETs. Methods: Clinical records of patients with completely resected TETs were retrospectively collected from 4 tertiary centers between January 2000 and February 2013. Information on the Masaoka–Koga stage was available for 1215 patients (M-K group), and 433 patients were classified according to the eighth edition of the Tumor-Node-Metastasis staging system (TNM group). Limited-stage and advanced-stage TETs were defined according to whether they were confined within the surrounding fatty tissues without invasion. The optimal cutoff value was selected using a maximally selected log-rank statistic. Results: The median tumor size was 6.0 ± 2.8 cm in the M-K group and 6.5 ± 3.0 cm in the TNM group. In the multivariable analysis, tumor size had a significant effect on both overall survival (P =.003) and recurrence-free survival (P <.001) for limited-stage tumors (M-K stage I or II or TNM stage I), but not for advanced-stage tumors (M-K stage III or IV or TNM stage II-IV; P =.349 for overall survival and P =.439 for recurrence-free survival). The optimal cutoff value for tumor size was >5.5 cm for both overall survival and recurrence-free survival in limited-stage TETs. Conclusions: Tumor size is an independent prognostic factor in patients with completely resected limited-stage TETs and a cutoff value >5.5 cm might help clinicians enact proper treatment strategies and surveillance.