Myasthenia Gravis and Prognosis of Thymoma: A Propensity Score Matching Trial

Abstract

Myasthenia Gravis (MG) occurs in approximately 30% of patients with thymoma. Although the relationship between MG and thymoma is depicted in a series of manuscripts, the association of the prognosis of thymoma and MG is still controversial. Distinctions of clinical characteristics and treatments between patients with and without MG is the possible interferences. To investigate whether MG is a dependent prognostic predictor in thymoma, we designed this propensity score matching trial. Patients pathologically diagnosed thymoma and MG were enrolled in MG group. Meanwhile, propensity score matched method was used to select patients in database of patients who diagnosed with thymoma without MG. Matched factors include sex, age, Masaoka stage, pathological subtypes and treatments including surgery, radiotherapy and chemotherapy. Matched patients were selected into nonMG group. Chi-square test is used to make a comparison of the characteristics of the two groups. Overall survival (OS), locoregional relapse free survival (LRFS), distant metastasis free survival (DMFS), progression free survival (PFS) and cancer specific survival (CSS) were calculated from the diagnosis of thymoma using Kaplan-Meier method. Between April 1992 and October 2018, two hundred and thirty-five patients were enrolled in Group MG and other 235 patients were matched in Group non-MG (1:1 ratio). There are 138 and 137 males in Group MG and Group non-MG respectively (P = 0.926). The median age of Group MG and Group non-MG was 45 years and 47 years old. There are 150 patients who were ≤50 years old in each group (P = 1.000). The WHO pathological subtypes were well balanced between the two groups (B2+B3:63.0% in MG and 63.4% in nonMG, P = 0.924). Most of the patients in both groups were with Masaoka stage I-III (MG vs. nonMG 90.2%vs.91.5%, P = 0.631). R0 resections were performed in 86.8% and 90.2% in MG and nonMG group (P = 0.247). The ratio of radiotherapy and chemotherapy delivery in MG and nonMG group were 43.4% vs. 39.1% (P = 0.349) and 12.3% and 17.9% (P = 0.094). The median follows up time of the two groups was 70.00 months (73.63months in MG group and 68.00 in nonMG group). At the last follow up, twenty-eight patients died in each group. Five patients died of myasthenic crisis without progression of thymoma. Five-year OS is 92.5% in MG group and 90.3% in non-MG group, 10-year OS were 80.2% vs81.4% (P = 0.632). None of PFS, DMFS and LRFS showed significant differences between MG and non-MG group and the details were showed in the table. MG is not an independent or direct prognostic factor of thymoma, although it might be helpful to get the diagnosis at early stage and brought better prognosis indirectly. Table: Association between MG and survivals.Abstract 2250; Table%nonMGMGP%nonMGMGPOS0.632PFS0.832 5y90.392.55y79.879.3 8y84.284.28y71.773.7 10y81.480.210y67.965.4LRFS0.613DMFS0.884 5y93.996.15y84.183.8 8y90.293.48y77.181.0 10y87.787.810y77.177.5CSS0.441 5y91.894.0 8y84.487.2 10y84.485.6 Open table in a new tab