Different View on Tumor Size Dilemma in Tumor-Node-Metastasis Staging System for Thymoma

Background Although tumor size is included in the definition of T descriptor in the tumor-node-metastasis (TNM) classification of many solid tumors, it is not considered for thymomas. This study aimed to assess the relationship of tumor diameters (the largest tumor diameter [LTD] and the mean tumor diameter [MTD]) with survival in thymoma patients undergoing surgical resection in a single center. Methods The study included 127 thymoma patients (age, 49.215.2 years; 65 males), who were evaluated based on pathological tumor sizes according to the LTD and MTD ([largest diameter+shortest diameter] / 2) and divided into three subgroups for each parameter as: patients with an LTD of <= 5cm, 5.1 to 10cm, and >10cm and patients with an MTD of <= 5, 5.1 to 10, and >10cm. Results In thymoma patients, survival significantly differed according to the presence of myasthenia gravis ( p =0.018), resection status (R0 or R1; p =0.001), T status ( p =0.015), and the Masaoka-Koga stage ( p =0.003). In the LTD subgroups, the overall survival of those with R0 resection was lower in those with an LTD of 5.1 to 10cm than in those with an LTD of <= 5cm ( p =0.051) and significantly lower in those with an MTD of 5.1 to 10cm than in those with an MTD of <= 5cm ( p =0.027). In the MTD subgroups, survival decreased as the tumor size increased. Conclusion Both smaller tumor size and complete resection are associated with better survival in thymoma patients. Therefore, the largest or the mean tumor size might be considered as a criterion in the TNM staging for thymoma.