Although lung cancer is the leading cause of cancer death in the U.S. in both men and women, it is also one of the most preventable kinds of cancer. At least four out of five cases are associated with cigarette smoking, and the cause-and-effect relationship has been extensively documented. During the 1920s, large numbers of men began to smoke cigarettes, presumably in response to increased advertising. Twenty years later, the frequency of lung cancer in men climbed sharply. In the 1940s, significantly more women became smokers. Twenty years later, there was a similar dramatic increase in lung cancer among women.
Lung tumors almost always start in the spongy, pinkish gray walls of the bronchi — the tubular, branching airways of the lungs. More than 20 types of cancerous tumors that originate in the lung itself — primary lung cancer — have been identified. The major types of lung cancer are small-cell lung cancer and non-small cell lung cancer. The more common non-small cell variety is further divided into squamous cell carcinoma, adenocarcinoma, large-cell carcinoma, and more. Mixed tumors may also occur.