Most lung cancers are found because a patient has symptoms, although some are detected through screening. Health insurers will cover periodic screening via low-dose CT scan for people with a history of heavy smoking. Screening can reveal lung cancers when they are still too small to cause symptoms and are more likely to be curable. If lung cancer is caught before it spreads, the likelihood of surviving five years increases to 60%.

Although only low-dose CT scans are recommended to screen for lung cancer, doctors who suspect lung cancer can use a chest X-ray, MRI, positron emission tomography scan or bone scan, which uses radioactive material to pin- point abnormal areas.

If any of those points to lung cancer, pathologists can look at the cells to determine whether they are cancerous. The cells can be from mucus coughed up from the lungs, fluid removed from the area around the lungs, or a needle or surgical biopsy of lung tissue.

If cancer is present, determining whether it has spread past the lungs can be revealed through additional tests: ultrasound of the lymph nodes; mediastinoscopy or mediastinotomy, which checks between the lungs; and thoracoscopy, which checks the spaces between the lungs and chest wall.

Patients with lung cancer should request that their treating physician conduct comprehensive biomarker, or genomic, testing of their tumor tissue, which can help determine which treatments are likely to be most effective. Genomic testing looks for altered genes that drive cancer and can be treated with targeted therapies. There are approved targeted therapies for alterations in these genes: EGFR, ALK, ROS1, RET, NTRK, MET and BRAF. Testing may also look for gene alterations that do not have approved therapies but have drugs being tested in clinical trials. Comprehensive biomarker testing includes looking at levels of certain proteins called PD-1 and PD-L1, which may influence whether a patient should receive immunotherapy.

Non-small cell lung cancer is divided into stages from 0, the least advanced, through 4, the most advanced. Small cell lung cancer is divided into two stages: limited and extensive.