Patterns and predictors of recurrence after radical resection of thymoma

Background: Recurrence of thymomas even after complete resection is common, but the relapse patterns remain controversial. This study aimed to define the patterns and predictors of relapse after complete resection of thymoma.

Methods: A single-institution retrospective study was performed with 331 patients who underwent radical resection of thymoma between 1991 and 2012.

Results: After a median follow-up of 59 months, the recurrence rate was 6.9% (23/331). Relapse occurred in 23 patients with the pleura (14) and tumor bed (6) as the most common sites of recurrence. According to the definitions of the International Thymic Malignancy Interest Group, 10 (43.5%) patients had local relapse, 15 (65.2%) had regional relapse, 10 (43.5%) had distant relapse. The difference in survival following relapse between lung and regional relapse was statistically significant (P=0.027) but that between lung and distant relapse was not (P=0.808). The recurrence rates correlated with the initial Masaoka stage. Further, recurrence also correlated with World Health Organization (WHO) tumor type. The recurrence-free survival rates in patients with tumor size ⩾8 cm were worse than those of patients with tumor size <8 cm (P=0.007). Tumor size was also correlated with stage (r=0.110). As tumor becomes larger, the stage is more advanced (P=0.023). Multivariate analysis showed that Masaoka stage (P=0.005), tumor size (P=0.033), and WHO histological type (P=0.046) were predictive factors of relapse.

Conclusion: Regional recurrence is the most common relapse pattern but local and distant relapse are also common. Advanced Masaoka stage, larger tumor size, and type B3 are risk factors of recurrence. Lung relapse should be considered distant relapse. Further, tumor size was correlated with Masaoka stage and therefore should be considered in the staging system.