[Cox multivariate analysis of prognosis and proposal on a modified staging system of thymoma]

To investigate the clinicopathologic features, prognostic factors and propose a new modified staging criteria for thymoma.

The data of 159 patients operated for thymoma collected were retrospectively analyzed as to their prognostic factors and criteria of clinical staging through comparison of survival rates by the actuarial method, Log-rank and Cox multivariable model.

Thorough resection (OR = 2.10), and extent of tumor invasion (OR = 1.73) were the most important prognostic factors. Tumor with peritumoral adhesion and absence of a complete capsule but without external invasion belonged to the criteria of stage II (II a). According to the prognosis and state of resection, lesions with obvious peritumoral invasion into the nearby organs but were thoroughly resected belonged to stage II (II b) and those incompletely resected belonged to III a. The unresectable lesions belonged to III b.

According to the Cox prognostic multivariable model, the criteria of clinical staging of thymoma are defined as: Stage I-completely encapsulated non-invasive tumor without tight fibrous adhesions to the surroundings. Stage II a-only capsular invasion or capsule incomplete or with tight fibrous adhesions to the surroundings. II b-invasion into the surrounding fatty tissue, pleura, partial pericardium or lung, Stage III a-invasion into the great vessels, heart, trachea or hilus, which are resected with difficulty, or only palliatively. III b-extensive invasion into the nearby organs, and resection is impossible. Stage IV a-pleural or pericardial dissemination, IV b-lymphatic or hematogenous metastasis.