Comparison of clinical features and prognosis between thymoma alone and thymoma with myasthenia gravis

Objective To investigate the clinicopathological features and prognosis in patients with thymoma and patients with thymoma and myasthenia gravis (MG). Methods A retrospective analysis was performed on the clinicopathological data of 161 patients pathologically diagnosed with thymoma alone or thymoma and MG from 2008 to 2014. In those patients, 128 had thymoma with MG and 33 had thymoma alone. The survival rates were calculated using the Kaplan-Meier method and analyzed using χ2 test or Fisher's exact probability test. Results The mean age of onset was 45.2 years for patients with thymoma and MG and 48.5 years for patients with thymoma alone. In patients with thymoma and MG, 74.2% had a tumor diameter of ≤5 cm, while 75.8% of patients with thymoma alone had a tumor diameter of ≥5 cm. According to the Masaoka staging system, 78.1% of patients with thymoma and MG had stage Ⅰ+ Ⅱ disease, while 51.1% of patients with thymoma alone had stage Ⅲ+ Ⅳ disease. There was no significant difference in the 3-year overall survival (OS) rate between the two groups (98.1% vs. 81.8%, P=1.000). The 5-year OS rate was significantly higher in patients with thymoma and MG than in patients with thymoma alone (91.1% vs. 42.9%, P=0.000). In all patients, 140 patients with complete resection had significantly higher 3-and 5-year OS rates than 21 patients with incomplete resection (97.2% vs. 58.8%, P=0.000; 92.7% vs. 25.0%, P=0.000). In patients with stage Ⅱ disease, there were no significant differences in the 3-or 5-year OS rates between patients with complete resection alone (n=25) and patients with complete resection and postoperative radiotherapy (n=25)(95% vs. 100%, P=1.000; 86% vs. 100%, P=0.467). Conclusions Compared with patients with thymoma alone, patients with thymoma and MG have an earlier age of onset, substantially smaller tumor diameters, and earlier Masaoka stages. MG and complete resection are positive prognostic factors for patients with thymoma. Radiotherapy after complete resection can reduce the recurrence rate in patients with stage Ⅱ disease. Key words: Thymoma; Myasthenia gravis; Clinicopathological features; Prognosis