Proposal of a novel system for the staging of thymic epithelial tumors.

Background: We designed and assessed a new TNM staging system (herein called the INT [Istituto Nazionale Tumori] system) for thymic epithelial tumors in order to overcome the perceived drawbacks of Masaoka's system, which represents the current standard.

Methods: In all, 123 cases were evaluated. The histologic types according to the World Health Organization (WHO) classification were as follows: subtype A: 5 cases; AB: 40; B1: 16; B2: 29; B3: 16; and C: 17 cases. There were 45 Masaoka's stage I, 33 stage II, 26 stage III, and 19 stage IV cases. A total of 11 INT definitions were grouped into three stages: locally restricted disease (75 cases), which included Masaoka's stage I and selected stage II cases (no pleural invasion); locally advanced disease (37 cases), which included Masaoka's stage III cases plus those staged II owing to pleural invasion and those staged IV owing to intrathoracic nodal or limited pleuropericardial involvement; and systemic disease (11 cases), which included the remaining Masaoka's stage IV cases.

Results: Completeness of resection, WHO types, and both staging systems were significant prognostic factors (p < 0.0001) on univariate analysis. The 95-month progression-free survival rates according to Masaoka's system were stage I: 100%; II: 93.6%; III: 46.3%; and IV: 23.2%. The INT system corresponding figures were as follows: locally restricted disease: 98.6%; locally advanced disease: 46.9%; and systemic disease: 11.7%. The INT system was the prognostic factor with the greatest impact (p = 0.0218) on multivariate analysis (Masaoka's system: p = 0.2012; completeness of resection: p = 0.6855; histology: p = 0.9386).

Conclusions: The INT system allows finer disease descriptions than Masaoka's system, resulting in a stage grouping with higher prognostic distinctiveness.