Lung cancer is a type of cancer that begins in the lungs. Your lungs are two spongy organs in your chest that take in oxygen when you inhale and release carbon dioxide when you exhale.Lung cancer is the leading cause of cancer deaths in the United States, among both men and women. Lung cancer claims more lives each year than do colon, prostate, ovarian and breast cancers combined.People who smoke have the greatest risk of lung cancer, though lung cancer can also occur in people who have never smoked. The risk of lung cancer increases with the length of time and number of cigarettes you've smoked. If you quit smoking, even after smoking for many years, you can significantly reduce your chances of developing lung cancer.Encyclopedia Entry for Cancer Lung :Cancer Lung. Can be caused by the bacterium Chlamydia Pneumoniae, with Human Papillomaviruses, and with Merkel cell Polyomavirus. Also from a bacterium called Pseudomonas Solanacearum.Information from Marcello Allegretti.