TNM is a clinical staging system for lung cancer. T, N, and M, respectively, represent the primary tumor size status, regional lymphatic metastasis status, and the presence or absence of distant metastasis. Clinical tumor staging is given according to the specifics of these three elements. Primary tumor (T) Tx: primary tumor size cannot be measured; or cancer cells found in sputum exfoliated cells, or bronchial washout fluid, but imaging and bronchoscopy do not reveal primary tumor; T0: no evidence of primary tumor Tis carcinoma in situ; T1a: primary tumor ≤2 cm in maximum diameter, confined to the lung and within the dirty pleura, not involving the main bronchus; or tumor confined to the tracheal wall, regardless of T1b: primary tumor >2cm, ≤3cm; T2a: tumor with any of the following conditions: maximum diameter >3cm, ≤5cm; involvement of the main bronchus, but the tumor is ≥2cm from the bulge; involvement of the dirty pleura; production of segmental or lobar atelectasis or obstructive pneumonia; T2b: tumor with any of the following conditions. T3: tumor of any size with one of the following conditions: primary tumor with maximum diameter >7 cm, involving the chest wall or diaphragm or mediastinal pleura, or bronchi (<2 cm from the rung, but not reaching the rung), or pericardium; producing total pulmonary atelectasis or obstructive pneumonia; satellite nodules in the same lung lobe of the primary tumor. T4: Tumor of any size that invades one of the following: heart, trachea, esophagus, trachea, mediastinum, bullae, or vertebrae; satellite nodes in different lobes of the lung ipsilateral to the primary tumor. Lymph node metastasis (N) Nx: lymph node metastasis cannot be determined; N0: no regional lymph node metastasis; N1: ipsilateral bronchial or hilar lymph node metastasis; N2: ipsilateral mediastinal and/or infralobar lymph node metastasis; N3: contralateral mediastinal and/or contralateral hilar, and/or ipsilateral or contralateral anterior oblique muscle or supraclavicular area lymph node metastasis. Distant metastasis (M) Mx: no distant metastasis could be evaluated; M0: no distant metastasis; M1a: pleural dissemination (malignant pleural effusion, pericardial effusion or pleural nodules); M1b: satellite nodules in the contralateral lobe of the primary tumor; distant metastasis (pulmonary/extra pleural). TNM staging of lung cancer (UICC 2009 version) Occult stage: TxN0M0 Stage 0: TisN0M0 T4N0-1M0 Stage Ia: T1N0M0 Stage Ib: T2aN0M0 Stage IIa: T1N1M0, T2bN0M0 Stage IIb: T2bN1M0 T3N0M0 T2aN1M0 Stage IIIa: T1-3N0M0 T3N1-2M0 III Stage b: T1-4N3M0 T4N2-3M0 Stage IV: T1-4N0-3M1