Lung cancer is a lung injury that begins in the lungs and may spread to lymph nodes or other organs in the body, such as the brain. Cancer from other organs also may spread to the lungs. Lung cancers usually are grouped into two main types called small cell and non-small cell (including adenocarcinoma and squamous cell carcinoma). These types of lung cancer grow differently and are treated differently. Non-small cell lung cancer is more common than small cell lung cancer. One of the most common causes and primary reason for lung cancer is cigarette smoking. There are chances that nonsmokers also get lung cancer. Smoke that enters the lungs causes damage to the lung tissue in which the body will try to repair the damage, but due to the continuous exposure, it will fail (includes second-hand smokers, those who around other smokers even though they don't smoke). Another causative agent is a radioactive gas called radon. Radioactive gas can enter through small holes in the buildings. Genetic mutation can increase the risk of developing lung cancer. There's no specific cure for lung cancers, but there are available treatment options. The most common treatment is chemotherapy, radiotherapy, and surgery. Some other therapies can be used, but targeted therapy drugs are also used to target the abnormalities in the affected cells there by killing the cancerous cells.