Oral 3.02: Postoperative survival for patients with thymoma complicating myasthenia gravis—chart experience

Background: To compare the postoperative survival between patients with thymoma only and those with both thymoma and MG.

Methods: The CHART registry recruited patients with thymoma from 16 centers over the country on an intention to treat basis from 1994 to 2012. Two groups were formed according to whether the patient complicated MG. Demographic and clinical data were reviewed, patients were followed and their survival status were analysed.

Results: There were 1,179 patients included in this study, including 206 with and 973 without MG. Complete thymectomy were done in 85.9% patients in MG group and 64.4% in non-MG group (P<0.05). There were more percentage of patients with the histology of tumors of thymoma AB, B1, or B2 (P<0.05) in MG group, and more percentage of patients with MG were in Masaoka’s stage I and II. The 20-year overall survival rates were 74.6% and 72.1% respectively (P=0.051). The survival rate was significantly higher in patients with MG when the histology was thymoma B3 or C (P=0.0083), or when the Masaoka’s staging was 3 or 4 (P=0.0089). Among patients with advanced stage thymoma (stage 3, 4a, 4b), the constituent ratios of 3, 4a, 4b were similar between MG and non-MG group. Histological, however, there were significantly more proportion of B1/B2 in the MG group while there were more B3/C in the non-MG group (P=0.000). Both groups were comparable in terms of resectability and postoperative recurrence, except that total thymectomy had been done in more proportion of patients in MG group (P=0.021). Multivariate analyses of Cox regression for all patients showed, Masaoka’s stage and resectability were strong independent prognostic indicators. Whereas in late Masaoka’s stage patients, MG and resectability were strong independent prognostic indicators. The OR for MG (yes) was 0.332 compared to non-MG (P=0.019).

Conclusions: The survival of patients with thymoma was superior when MG was present, especially in late Masaoca’s stage patients. Possible reasons included early diagnosis of the tumor, better pathologic types and more attention for complete thymectomy in this group.

Keywords: Thymoma; myasthenia gravis; survival