| Stage | Koga et al. [5] | Detterbeck et al. [24] |
| I | Grossly and microscopically completely encapsulated tumour | Invasion into but not through the capsule In the absence of capsule, absence of invasion into surrounding tissues |
| IIa | Microscopic transcapsular invasion | Microscopic transcapsular invasion (not grossly appreciated) |
| IIb | Macroscopic invasion into thymic or surrounding fatty tissue, or grossly adherent to but not breaking through the mediastinal pleura or pericardium | Gross extension into normal thymus or perithymic fat surrounding the tumour (microscopically confirmed) Adherence to pleura or pericardium, with microscopic confirmation of perithymic invasion |
| III | Macroscopic 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) |
| IVa | Pleural or pericardial metastasis | Microscopically confirmed separate nodules in the visceral or parietal pleural, pericardial or epicardial surfaces |
| IVb | Lymphogenous or haematogenous metastasis | Any 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].