Table 1. TNM (tumour, node, metastasis) classification for lung cancer.

Primary tumour (T)
TX	Primary tumour cannot be assessed, or the tumour is proven by the presence of malignant cells in sputum or bronchial washing but is not visualised by imaging or bronchoscopy
T0	No evidence of primary tumour
Tis	Carcinoma in situ
T1	Tumour ≤3 cm in greatest dimension, surrounded by lung or visceral pleura, no bronchoscopic evidence of invasion, more proximal than the lobar bronchus (not in the main bronchus); superficial spreading of tumour in the central airways (confined to the wall of the trachea or mainstem bronchus)
T1a	Tumour ≤2 cm in the greatest dimension
T1b	Tumour >2 cm but ≤3 cm in the greatest dimension
T2	Tumour >3 cm but ≤7 cm or tumour with any of the following:     Invades visceral pleura     Involves the main bronchus ≥2 cm distal to the carina     Associated with atelectasis/obstructive pneumonitis extending to hilar region but not involving the entire lung
T2a	Tumour >3 cm but ≤5 cm in the greatest dimension
T2b	Tumour >5 cm but ≤7 cm in the greatest dimension
T3	Tumour >7 cm or one that directly invades any of the following:     Chest wall (including superior sulcus tumours), diaphragm, phrenic nerve, mediastinal pleura, or parietal pericardium     Tumour in the main bronchus <2 cm distal to the carina but without involvement of the carina     Associated atelectasis/obstructive pneumonitis of the entire lung or separate tumour nodule(s) in the same lobe
T4	Tumour of any size that invades any of the following: mediastinum, heart, great vessels, trachea, recurrent laryngeal nerve, oesophagus, vertebral body, or carina Separate tumour nodule(s) in a different ipsilateral lobe
Regional lymph nodes (N)
NX	Regional lymph nodes cannot be assessed
N0	No regional node metastasis
N1	Metastasis in ipsilateral peribronchial and/or ipsilateral hilar lymph nodes and intrapulmonary nodes, including involvement by direct extension
N2	Metastasis in the ipsilateral mediastinal and/or subcarinal lymph node(s)
N3	Metastasis in the contralateral mediastinal, contralateral hilar, ipsilateral or contralateral scalene, or supraclavicular lymph nodes
Distant metastasis (M)
MX	Distant metastasis cannot be assessed
M0	No distant metastasis
M1	Distant metastasis
M1a	Separate tumour nodule(s) in a contralateral lobe; tumour with pleural nodules or malignant pleural (or pericardial) effusion
M1b	Distant metastasis

Reproduced from [18] with permission from the publisher.