Smoking is by far the leading risk factor for lung cancer. Cigarette smoke contains more than 6,000 components, many of which lead to DNA damage (see table of tobacco-related DNA damages in Tobacco smoking).
Other causes include radon, exposure to secondhand smoke, exposure to substances such as asbestos, chromium, nickel, beryllium, soot, or tar, family history of lung cancer, and air pollution.
In general, DNA damage appears to be the primary underlying cause of cancer. Though most DNA damages are repairable, leftover un-repaired DNA damages from cigarette smoke are the likely cause of NSCLC.
DNA replication past an un-repaired damage can give rise to a mutation because of inaccurate translesion synthesis. In addition, during repair of DNA double-strand breaks, or repair of other DNA damages, incompletely cleared sites of repair can lead to epigenetic gene silencing.
Many of the symptoms of NSCLC can be signs of other diseases, but having chronic or overlapping symptoms may be a signal of the presence of the disease. Some symptoms are indicators of less advanced cases while some may signal that the cancer has spread. Some of the symptoms of less advanced cancer include chronic cough, coughing up blood, chest pain, hoarseness, shortness of breath, wheezing, chest pain, weight loss, and loss of appetite. A few more symptoms associated with the early progression of the disease are feeling weak, being very tired, having trouble swallowing, swelling in the face or neck, and continuous or recurring infections like bronchitis or pneumonia. Signs of more advanced cases include bone pain, nervous system changes (headache, weakness, dizziness, balance problems, seizures), jaundice, lumps near the surface of the body, numbness of extremities due to Pancoast Syndrome, and nausea, vomiting and constipation brought on by hypercalcemia. Some more of the symptoms that indicate further progression of the cancer include shortness of breath, superior vena cava syndrome, trouble swallowing, large amounts of mucus, weakness, fatigue, and hoarseness.