Abstract: Objective The aim of this study was to evaluate the effect of myasthenia gravis(MG)on the prognosis of patients with thymoma after surgery,and to analyze other related factors affecting the prognosis of patients with thymoma after surgery. Methods The clinical data of 187 thymoma patients in the 8th Medical Center of the Chinese People's Liberation Army from September 2002 to January 2018 were retrospectively analyzed.Among them,139 thymoma patients complicated with myasthenia gravis(MG group)and 48 patients with simple thymoma(non-MG group).The 1∶1 nearest neighbor matching method was used to perform propensity score matching(PSM)for the two groups to achieve equilibrium within covariance.Kaplan-Meier method was used to calculate the survival rate,and log-rank test was preformed to analyze the differences in survival rates between MG and non-MG groups.Cox proportional hazard regression model was used for univariate and multivariate analyses for overall thymoma patients after surgery. Results Before the results were matched,the gender(χ²=4.180,P=0.041),age of diagnosis(χ²=8.590,P=0.003),WHO histological subtype(χ²=4.764,P=0.029)and postoperative adjuvant chemotherapy(χ²=5.627,P=0.018)were significantly different between the MG group(n=139)and the non-MG group(n=48).The 5-year overall survival rates of patients in the MG group and non-MG group were 92.4% and 69.6%,respectively,and the difference was statistically significant(Log-rank test,P=0.002).After matching by the PSM method,a total of 44 of patients were successfully matched in the two groups,and there was no significantly difference in clinical baseline data between the MG and non-MG groups(P＞0.05).The 5-year overall survival rates of patients in the MG group and non-MG group patients were 90.8% and 67.3%,respectively,and the difference was statistically significant(Log-rank test,P=0.015).Univariate analysis for patients with overall thymoma surgery showed that Masaoka stage(HR=0.237,95% CI:0.111~0.504,P＜0.001),resection status(HR=0.250,95% CI:0.096~0.654,P=0.005),postoperative adjuvant chemotherapy(HR=0.367,95% CI:0.179~0.751,P=0.006)and MG(HR=0.336,95% CI:0.162~0.669,P=0.003)might be associated with survival prognosis of thymoma patients after surgery.Cox multivariate analysis showed that Masaoka stage was an independent prognostic factor affecting the survival of thymoma patients after surgery(HR=0.317,95% CI:0.140~0.720,P=0.006),and MG affected protective survival factors of thymoma patients after surgery(HR=0.445,95% CI:0.204~0.971,P=0.042). Conclusion For patients with operable thymoma,thymoma patients with MG have a better prognosis than those without MG.Masaoka stage is an independent prognostic factor that affects the survival of thymoma patients.

Key words: Thymoma, Myasthenia gravis, Paraneoplastic syndrome, Prognosis, Propensity score matching