Clinical Investigation of Resected Patients with Thymoma Based on the WHO Classification

Objective. The therapeutic usefulness of the WHO classification of thymoma was evaluated. Methods. Fifty-one patients with thymomas (male: 30, female: 21) underwent a resection between 1990 to 2005 at this institution. These patients were categorized according to both the WHO classification and the Masaoka staging system. The patients with Type C thymomas were excluded from this study. Results. According to the WHO classification the 51 patients were categorized as Type A-1 patient (2.0%), AB-18 (35.3), B1-16 (31.4), B2-11 (21.6), B3-5 (9.8), while according to the Masaoka staging the classification was stage I-30 (58.8), II-7 (13.7), III-10 (19.6), IVa-3 (5.9), IVb-1 (2.0). The total number of patients with Type A, AB, and B1 accounted for 81.1% of patients with Masaoka stage I and II, Type B2 and B3 patients accounted for 64.3% of patients with Masaoka stage III and IV. The 5- and 10- year survival rates of the patients based on the WHO classification were as follows; Type A-100%, 100%, AB-100%, 90.0%, B1-88.9%, 88.9%, B2-83.3%, 41.7%, respectively, while in Type B3 the 4-year survival rate was 66.7%. The 5- and 10- year survival rates of the patients with groups of Type A/AB/B1 and Type B2/B3 were 95.7%, 89.7% and 77.4%, 38.7%, respectively. Although no significant difference in the survival rate was observed between the 2 groups, Type B2/B3 group tended to have a poor prognosis in comparison to the Type A/AB/B1 group. Tumor recurrence was identified in 6 (12.8%) out of 47 patients with a complete resection. Whereas 1 (2.9%) of 34 patients of Type A/AB/B1 showed a recurrence and the number of recurrent Type B2/B3 lesions was 5 (38.5%) of 13 patients. There was no prognositc difference between the groups of Type A/AB/B1 and Type B2/B3 according to Masaoka stages I and II. However, in Masaoka stage III and IV thymomas, the survival rate of the patients with Type B2/B3 was significantly poorer than that of Type A/AB/B1 (p=0.03). Conclusions. A distinction between the groups with Type A/AB/B1 and Type B2/B3 thymomas based on the WHO classification may be useful for predicting both recurrence as well as the prognosis in a resected thymoma. In addition, this grouping is considered to play a more important prognostic role in the patients with Masaoka stage III and IV thymomas than in those with stage I and II thymomas.<br>