Table 2. The Masaoka–Koga International Thymic Malignancy Interest Group staging system
StageKoga et al. [5]Detterbeck et al. [24]
IGrossly and microscopically completely encapsulated tumourInvasion into but not through the capsule
In the absence of capsule, absence of invasion into surrounding tissues
IIaMicroscopic transcapsular invasionMicroscopic transcapsular invasion (not grossly appreciated)
IIbMacroscopic invasion into thymic or surrounding fatty tissue, or grossly adherent to but not breaking through the mediastinal pleura or pericardiumGross extension into normal thymus or perithymic fat surrounding the tumour (microscopically confirmed)
Adherence to pleura or pericardium, with microscopic confirmation of perithymic invasion
IIIMacroscopic invasion into neighbouring organ (i.e. pericardium, great vessel or lung)Microscopic invasion of the mediastinal pleura (either partial or penetrating the elastin layer)
Microscopic invasion of the pericardium (either partial in the fibrous layer or penetrating through to the serosal layer)
Microscopically confirmed direct penetration into the outer elastin layer of the visceral pleura or into the lung parenchyma
Invasion into the phrenic or vagus nerves (microscopically confirmed)
Invasion into or penetration through major vascular structures (microscopically confirmed)
Adherence (i.e. fibrous attachment) of lung or adjacent organs only if there is mediastinal pleural or pericardial invasion (microscopically confirmed)
IVaPleural or pericardial metastasisMicroscopically confirmed separate nodules in the visceral or parietal pleural, pericardial or epicardial surfaces
IVbLymphogenous or haematogenous metastasisAny nodal involvement (e.g. anterior mediastinal, intrathoracic, low/anterior cervical nodes or any other extrathoracic nodes)
Distant metastases (i.e. extrathoracic and outside the cervical perithymic region) or pulmonary parenchymal nodules (not a pleural implant)
  • Adapted from [5] and [24].