Myasthenia gravis in patients with thymoma affects survival rate following extended thymectomy

Abstract

Thymomas are the most common adult tumors in the anterior mediastinal compartment, and a significant amount of thymomas are complicated by myasthenia gravis (MG). Extended thymectomy (ET) is the primary treatment method for thymomas and is used to completely resect possible ectopic thymus to avoid recurrence. Studies on the effect of MG in thymoma patients following ET are limited. The aim of the present study was to determine whether the presence of MG affects the prognosis of patients with thymoma. The present study consisted of 104 patients with thymoma that underwent ET; 61 men (58.7%) and 43 women (41.3%) (mean age, 54.6 years). In total, 38 patients had MG (36.5%). MG was most frequently observed in World Health Organization (WHO) classification type B2 thymoma compared with other types of thymoma. During the 5-year follow-up period, 11 patients succumbed to a recurrence of thymoma or respiratory failure due to MG. The overall 5-year survival rate in patients without MG or with MG was 89.1 and 76.0%, respectively. The overall survival (OS) rate in patients with Masaoka stages I + II and III + IV was 90.0 and 68.0%, respectively. The OS rate in patients with WHO type A + AB + B1 and type B2 + B3 was 96.9 and 76.8%, respectively. The patients with MG (P=0.026), Masaoka stages III + IV (P=0.008) and WHO type B2 + B3 (P=0.032) had a poorer prognosis compared with patients without these characteristics. Furthermore, multivariate analysis by Cox regression revealed that age [P=0.032; relative risk (RR)=1.097; 95% confidence interval (CI)=1.097-1.192] and MG (P=0.042; RR=0.167; 95% CI=0.037-0.940) significantly affected OS rate. In summary, ET is a reliable method for the treatment of thymoma. Long-term survival is expected for patients at early Masaoka stages, and for patients without MG. The prognosis of patients with thymomas with MG is poorer compared with patients without MG. The present findings provide useful information for the future management of patients with thymomas.

Keywords: extended thymectomy; myasthenia gravis; survival analysis; thymoma.

Figure 1.

Tumor size divided according to Masaoka stage or WHO histological classification. (A) Association between tumor size and Masaoka stage. The tumor size in Masaoka stage I and II was significantly smaller compared with stages III and IV (P<0.001). (B) Association between tumor size and WHO histological classification. WHO, World Health Organization.

Figure 2.

Overall survival curves following surgery according to MG diagnosis, Masaoka stage and WHO histological classification. (A) The overall survival rates in patients with and without MG; (B) the overall survival rates in patients according to Masaoka stage; (C) the overall survival rates in patients according to WHO histological classification. MG, myasthenia gravis; WHO, World Health Organization.