What are some causes of lung cancer?

Risk factors. Lung cancer is most commonly a long process of years in which the lungs are exposed to damaging substances/"carcinogens". The biggest/best known is smoking. This link may help: http://www.Cancer.Net/cancer-types/lung-cancer/risk-factors-and-prevention.
SMOKING SMOKING . And smoking the biggest and most significant risk factor. 90% of lung cancers develop in people who have smoked. Other causes: asbestos exposure, radon.
Smoking! Smoke from cigarettes contains approximately 35 known chemicals to cause tumors in lab rats. Smokers have a much higher incidence of lung cancer over the non-smoking population. Asbestos inhalation increases risk for mesothelioma, a very aggressive form of lung cancer. Radon, a radioactive decay product from soil uranium, is thought to be the second leading cause of lung cancer in the usa.