Objectives: Thymoma is a relatively rare tumour and is uniquely associated with autoimmune diseases such as myasthenia gravis (MG). However, the factors involved in the prognosis of thymoma remain under discussion.
Methods: We retrospectively reviewed 162 patients who underwent extended thymectomy via median sternotomy for thymoma at our institute from 1976 to 2009. The histological subtype was classified according to the World Health Organization (WHO) histological classification system. Survival analysis was performed using the Kaplan-Meier method and the Cox proportional hazards model.
Results: Tumours comprised 7 Type A tumours, 38 Type AB, 49 Type B1, 45 Type B2 and 23 Type B3. Various types of autoimmune diseases were comorbid in 66 patients. The median follow-up period was 94 months, and 14 patients experienced recurrence. Seven patients died of recurrent tumour, and 18 patients died of causes other than thymoma. The 10-year overall survival was 85.7%, and the 10-year disease-free survival (DFS) was 76.8%. The 10-year DFS was 62.5% for Type A, 86.3% for Type AB, 91.5% for Type B1, 77.1% for Type B2 and 26.3% for Type B3. In multivariate analysis, age, Type B3 and MG were determined as prognostic factors for survival. On the other hand, Masaoka's stage did not influence survival.
Conclusions: Type B3 classified by the WHO histological classification system is a poor prognostic factor for survival of thymoma after extended thymectomy. Association with MG is possibly an indicator of poor survival. Age is an independent prognostic factor, suggesting favourable prognosis of thymoma after surgical treatment. Considering thymoma is a rare tumour, it would be necessary to build a multi-institutional database as soon as possible.