Key Points for This Section

Lung cancer is a disease in which malignant (cancer) cells form in the tissues of the lung. Lung cancer is the leading cause of cancer death in the United States. Tobacco smoking is the most important risk factor for lung cancer.

Lung cancer is a disease in which malignant (cancer) cells form in the tissues of the lung.

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. The left lung has two lobes. The right lung, which is slightly larger, has three. A thin membrane called the pleura surrounds the lungs. Two tubes called bronchi lead from the trachea (windpipe) to the right and left lungs. The bronchi are sometimes involved in lung cancer. Small tubes called bronchioles and tiny air sacs called alveoli make up the inside of the lungs.

There are two types of lung cancer: small cell lung cancer and non-small cell lung cancer.

See the following PDQ summaries for more information about lung cancer:

• Lung Cancer Prevention ¹
• Non-Small Cell Lung Cancer Treatment ²
• Small Cell Lung Cancer Treatment ³

Lung cancer is the leading cause of cancer death in the United States.

Lung cancer is the leading cause of cancer death and the most common nonskin cancer in men and women combined in the United States.

Tobacco smoking is the most important risk factor for lung cancer.

Anything that increases a person's chance of developing a disease is called a risk factor. The main cause of lung cancer is tobacco use, including smoking cigarettes, cigars, or pipes, now or in the past.

There are other risk factors for lung cancer, but even when taken together, their effect on lung cancer is very small compared to the effect of tobacco smoking. These include the following:

• Being exposed to second-hand smoke.
• Being exposed to asbestos, arsenic, chromium, nickel, or other workplace agents.
• Being exposed to radon, which can be found in the home as well as in the workplace.

Glossary Terms

Tiny air sacs at the end of the bronchioles in the lungs.

A poisonous chemical used to kill weeds and pests. Also used in cancer therapy.

A group of minerals that take the form of tiny fibers. Asbestos has been used as insulation against heat and fire in buildings. Loose asbestos fibers breathed into the lungs can cause several serious diseases, including lung cancer and malignant mesothelioma (cancer found in the lining of the lungs, chest, or abdomen). Asbestos that is swallowed may cause cancer of the gastrointestinal tract.

The large air passages that lead from the trachea (windpipe) to the lungs.

A tiny branch of air tubes in the lungs.

A portion of an organ, such as the liver, lung, breast, thyroid, or brain.

One of a pair of organs in the chest that supplies the body with oxygen, and removes carbon dioxide from the body.

Cancer that forms in tissues of the lung, usually in the cells lining air passages. The two main types are small cell lung cancer and non-small cell lung cancer. These types are diagnosed based on how the cells look under a microscope.

A group of lung cancers that are named for the kinds of cells found in the cancer and how the cells look under a microscope. The three main types of non-small cell lung cancer are squamous cell carcinoma, large cell carcinoma, and adenocarcinoma. Non-small cell lung cancer is the most common kind of lung cancer.

A part of the body that performs a specific function. For example, the heart is an organ.

PDQ is an online database developed and maintained by the National Cancer Institute. Designed to make the most current, credible, and accurate cancer information available to health professionals and the public, PDQ contains peer-reviewed summaries on cancer treatment, screening, prevention, genetics, complementary and alternative medicine, and supportive care; a registry of cancer clinical trials from around the world; and directories of physicians, professionals who provide genetics services, and organizations that provide cancer care. Most of this information, and more specific information about PDQ, can be found on the NCI's Web site at http://www.cancer.gov/cancertopics/pdq. Also called Physician Data Query.

A thin layer of tissue that covers the lungs and lines the interior wall of the chest cavity. It protects and cushions the lungs. This tissue secretes a small amount of fluid that acts as a lubricant, allowing the lungs to move smoothly in the chest cavity while breathing.

A radioactive gas that is released by uranium, a substance found in soil and rock. Breathing in too much radon can damage lung cells and may lead to lung cancer.

Something that increases the chance of developing a disease. Some examples of risk factors for cancer are age, a family history of certain cancers, use of tobacco products, being exposed to radiation or certain chemicals, infection with certain viruses or bacteria, and certain genetic changes.

An aggressive (fast-growing) cancer that forms in tissues of the lung and can spread to other parts of the body. The cancer cells look small and oval-shaped when looked at under a microscope.

The airway that leads from the larynx (voice box) to the bronchi (large airways that lead to the lungs). Also called windpipe.