The lungs have extensive networks of blood and lymph vessels. Cancer cells may grow into these vessels and be carried by the blood or lymph to circulate through the body. The cancer cells may then be deposited in other organs of the body. It is also possible for cancer cells that begin in other organs to spread to the lungs.

Smoking is the number one cause of lung cancer. Cigarette smoke contains more than 4,000 different chemicals, many of which are proven carcinogens, while hundreds of others increase the cancer-causing power of carcinogens. Many of these chemicals also affect the nonsmoker inhaling secondary smoke. Men who smoke are estimated to be 22 times more likely to develop lung cancer than those who do not, while women who smoke are estimated to be 12 times more likely, If you stop smoking, the risk of cancer decreases steadily each year as abnormal cells are replaced by normal cells. 

Another leading cause of lung cancer is on-the-job exposure to carcinogens. Asbestos is perhaps the best known of the industrial substances associated with lung cancer, but there are many cancer-causing substances such as asbestos, uranium, arsenic, and certain petroleum products, that people may deal with at work. Lung cancer occurs most often in people over 50 who have long histories of cigarette smoking.

Symptoms of lung cancer include, chronic cough, coughing up blood, wheezing and chest pain. 

The doctor may do a bronchoscopy to look inside the bronchial tubes and lungs. A bronchoscope is a small tube inserted through the nose or mouth, down the throat, into the bronchial tubes. He may follow this up with a biopsy of lung tissue or of the lymph nodes between the lungs. X-rays and test of sputum also reveal lung cancer. 

Surgery may cure lung cancer. Radiation therapy in combination with chemotherapy is also used to treat lung cancer.