Skip to content
My WebMD Sign In, Sign Up

What Is Lung Cancer?

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 Cancer

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.

Non-Small Cell Lung Cancer

Squamous cell carcinoma usually starts in cells of the central bronchi, the largest branches of the bronchial tree. It accounts for 30% of lung cancers, and occurs more commonly in men and in smokers. It's the easiest to detect early, since its distinctive cells are likely to show up in tests of mucus samples. It also tends to be most curable if found early because it spreads relatively slowly and often does not spread outside of the lung.

Adenocarcinoma is the most common type of lung cancer accounting for 40% of all cases with its incidence increasing. This type of lung cancer occurs mainly in current or former smokers, but it is also the most common type of lung cancer seen in non-smokers. Also, it's more common in women than in men, and it is more likely to occur in younger people than other types of lung cancer. Adenocarcinoma tends to spread to the lymph nodes and distant organs. It's commonly a mixed type of tumor and may cause no symptoms initially.   

Large-cell carcinomas are a group of cancers with large, abnormal-looking cells that tend to originate along the outer edges of the lungs. They are the least common of the non-small cell lung cancers accounting for 10%-15% of all cases. However, this type of tumor has a high tendency to spread to nearby lymph nodes and distant sites.

Lung Cancer Risks: Myths vs. Facts

Can vitamins protect you? Is it too late to quit smoking? Bust the myths.
View slideshow