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Table 1 Masaoka staging system

From: Ectopic thymoma of the lung; a rare case report and review of the literature

Masaoka staging system [7]  
STAGE I Macroscopically encapsulated with no microscopically detectable capsular invasion.
STAGE II Macroscopic invasion of mediastinal fatty tissue or mediastinal pleura or microscopic invasion into the capsule.
STAGE III Macroscopic invasion into surrounding structures
(pericardium, great vessels, lung).
STAGE IV (A) Pleural or pericardial dissemination.
  (B) Lymphogenous or hematogenous metastases.