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Thymoma Staging System of Masaoka 1994a

Stage Description 
IMacroscopically, completely encapsulated; microscopically, no capsular invasion.
IIMacroscopic invasion into surrounding fatty tissue or mediastinal pleura; microscopic invasion into capsule.
IIIMacroscopic invasion into neighboring organs (pericardium, lung, and great vessels).
IVaPleural or pericardial dissemination.
IVbLymphogenous or hematogenous metastases.


  1. Nakagawa K, Asamura H, Matsuno Y, et al.: Thymoma: a clinicopathologic study based on the new World Health Organization classification. J Thorac Cardiovasc Surg 126 (4): 1134-40, 2003.  [PUBMED Abstract]