Primary Tumor (T) Tx: primary tumor cannot be determined, or sputum cytology and bronchial washings reveal cancer cells but no tumor is seen on bronchoscopy; T0: no evidence of primary tumor; carcinoma in situ; T1: tumor less than or equal to 3 cm in diameter, surrounded by lung tissue or dirty pleura, confined to lobe bronchi; T1a: tumor less than or equal to 2 cm in diameter; T1a: tumor greater than or equal to 2 cm in diameter T1b: tumor diameter greater than 2cm but less than or equal to 3cm; T2: tumor diameter greater than 3cm but less than or equal to 7cm, or any tumor with any of the following characteristics: 1. involving the main bronchus but greater than or equal to 2cm from the bulge; 2. invading the dirty pleura (PL1 or PL2); 3. complicating pulmonary atelectasis or obstructive pneumonia beyond the hilum but not total pulmonary atelectasis). T2a: tumor diameter greater than 3cm but less than or equal to 5cm; T2b: tumor diameter greater than 5cm but less than or equal to 7cm; T3: tumor diameter greater than 7cm or direct invasion of the following structures: 1.mural pleura (PL3), chest wall (including supraglottic sulcus), diaphragm, phrenic nerve, mediastinal pleura, pericardial wall; 2.located in the main bronchus (less than or equal to 2cm from the bulge but not directly invading the bulge) T4: Tumor of any size, invading any of the following structures: mediastinum, heart, great vessels, trachea, recurrent laryngeal nerve, vertebral body, bulge, and tumor nodes found in different lobes of the same lung. Nx: regional lymph node metastasis cannot be determined; N0: no regional lymph node metastasis; N1: tumor metastasis to ipsilateral peribronchial and/or ipsilateral hilar and pulmonary artery lymph nodes, including direct invasion; N2: tumor metastasis to ipsilateral mediastinum and/or inferior bulbar lymph nodes; N3: tumor metastasis to contralateral mediastinum, contralateral hilar, ipsilateral or contralateral oblique muscle, or clavicle. N3: tumor metastasis to the contralateral mediastinum, contralateral hilar, ipsilateral or contralateral oblique muscle, or supraclavicular lymph nodes. M0: no distant metastasis; M1: distant metastasis: M1a: metastatic nodules and pleural nodules in the contralateral lobe, or malignant pleural (or pericardial) effusion; M1b: distant metastasis. Most patients with lung cancer have pleural and pericardial exudate due to tumor. However, there are a few patients with pleural and pericardial exudates in which no cancer cells are found on multiple cytopathological examinations and the exudate is non-hematogenous and non-exudative. When these conditions are present and the clinical judgment is that the exudate is not caused by tumor, the exudate cannot be used as a staging factor and the patient should be classified as M0.