After finding a lump in the lung, many patients ask whether it is lung cancer. How to confirm the diagnosis of lung cancer becomes a concern for patients. The diagnosis of lung cancer can be confirmed by seeing cancer cells or cancerous tissues under microscope. 1.Patients with cough and sputum, especially bloody sputum may have cancer cells shed into the sputum, so sputum can be considered to find tumor cells to confirm the diagnosis. 2.Patients with pleural effusion in advanced stage may have cancer cells shed into the chest cavity and cause chest implantation to produce pleural fluid. For central type lung cancer, since it can be detected by electronic fiberoptic bronchoscopy, it can be diagnosed by biopsy under electronic fiberoptic bronchoscopy. For peripheral lung cancer, CT-guided aspiration biopsy can be considered; for those with close relationship with chest wall, ultrasound-guided aspiration biopsy can be considered. 5.For advanced lung cancer with enlarged lymph nodes in the neck, cervical lymph node dissection or puncture biopsy can be performed to confirm the diagnosis. 6. For enlarged mediastinal lymph nodes, ultrasound bronchoscopic aspiration biopsy or mediastinoscopic biopsy can be considered. 7.For small lesions that are difficult to bronchoscopic biopsy or aspiration biopsy, and there is no contraindication to surgery, surgical local excision can be considered and sent for rapid frozen pathology to confirm the diagnosis. 8.For those who have pleural effusion and have difficulty in detecting the lesion, medical thoracoscopy or surgical thoracoscopic exploration and biopsy can be considered. 9.Cytological examination can clarify the diagnosis, but genetic testing cannot be done. Biopsy is the histological confirmation of diagnosis, and sufficient specimens can be obtained for molecular diagnosis. There are various methods to confirm the diagnosis of lung cancer. However, it is necessary to obtain sufficient diagnostic information to guide treatment while causing as little trauma to patients as possible. This requires a rational choice of diagnostic tools.