Myasthenia gravis affects overall survival in patients with thymoma: an analysis of multicentre database using propensity score matching.

OBJECTIVES About one-third of patients with thymoma have myasthenia gravis (MG). It remains controversial whether MG affects the prognosis of patients with thymoma. The aim of this study was to evaluate the effect of MG on the prognosis of patients with thymoma in a multicentre database. METHODS Patients with thymoma who underwent thymectomy were identified from 2 prospectively collected databases in 2 medical centres from 2010 to 2018. Kaplan-Meier curves and the log-rank test were used to assess overall survival and recurrence-free survival, and a Cox proportional hazards model was used to determine significant contributors to survival. Propensity score matching was performed to eliminate selection bias. RESULTS A total of 514 patients with thymoma were included in this study, of whom 320 patients were MG-free and 194 had MG. Patients with MG were younger (median age 50 vs 54 years, P = 0.001) and had smaller tumours (4.4 ± 2.0 vs 4.9 ± 2.3 cm, P = 0.020). Pathological analysis showed that type B tumours especially B2-B3 (B2 + B3 + mix B tumours, 55.2%) are more common in patients with MG, while type AB (37.2%) was the most common in patients without MG. A larger proportion of Masaoka III-IV stage tumour (25.7% vs 11.0%, P < 0.001) was seen in patients with thymoma and MG. Multivariable Cox regression analysis demonstrated that MG (hazard ratio [HR] = 3.729, 95% confidence interval [CI]: 1.398-9.947, P = 0.009), incomplete resection (HR = 5.441, 95% CI: 1.500-19.731, P = 0.010) and Masaoka stage III + IV (HR = 3.390, 95% CI: 1.196-9.612, P = 0.022) were negative prognostic factors of overall survival. Meanwhile, MG (HR =3.489, 95% CI: 1.403-8.680, P = 0.007) and Masaoka stage III + IV (HR = 6.582, 95% CI: 2.575-16.828, P < 0.001) were negative prognostic factors of recurrence-free survival. Propensity-matched analysis compared 148 patient pairs. K-M survival analysis demonstrated that MG was associated with worse overall survival and recurrence-free survival in propensity score-matched patients (log-rank, P = 0.034 and 0.017, respectively). CONCLUSIONS Thymoma patients with MG have smaller tumours and a higher percentage of late-stage tumours, which are mainly of WHO B types, especially B2-B3 types. In addition, MG is significantly associated with worse overall survival and recurrence-free survival in thymoma.