Overview The lungs are a pair of cone-shaped breathing organs inside the chest. The lungs bring oxygen into the body when breathing in and send carbon dioxide out of the body when breathing out. Each lung has sections called lobes. Two tubes called bronchi lead from the trachea (windpipe) to the lungs. The two main types of lung cancer are non-small cell lung cancer and small cell lung cancer. The types are based on the way the cells look under a microscope. Non-small cell lung cancer is much more common than small cell lung cancer. Tobacco smoking is the most common cause of lung cancer. Lung cancer is the leading cause of death from cancer in the U.S. and the number of deaths from lung cancer in women is increasing. For most patients with lung cancer, current treatments do not cure the cancer.Anatomy of the respiratory system, showing the trachea and both lungs and their lobes and airways.