Small cell 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 that are found within the chest. The lungs bring oxygen into the body when breathing in and take out carbon dioxide 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 also involved in lung cancer. Small tubes called bronchioles and tiny air sacs called alveoli make up the inside of the lungs.

Anatomy of the respiratory system, showing the trachea and both lungs and their lobes and airways. Lymph nodes and the diaphragm are also shown. Oxygen is inhaled into the lungs and passes through the thin membranes of the alveoli and into the bloodstream (see inset).

There are two types of lung cancer: small cell lung cancer and non-small cell lung cancer. This summary provides information on small cell lung cancer. (See the PDQ summary on Non-Small Cell Lung Cancer Treatment for more information.)

There are three types of small cell lung cancer.

These three types include many different types of cells. The cancer cells of each type grow and spread in different ways. The types of small cell lung cancer are named for the kinds of cells found in the cancer and how the cells look when viewed under a microscope:

• Small cell carcinoma (oat cell cancer).
• Mixed small cell/large cell carcinoma.
• Combined small cell carcinoma.

Smoking tobacco is the major risk factor for developing small cell lung cancer.

Anything that increases your chance of getting a disease is called a risk factor. Having a risk factor does not mean that you will get cancer; not having risk factors doesn’t mean that you will not get cancer. People who think they may be at risk should discuss this with their doctor. Cigarette smoking is the most common cause of lung cancer. Risk factors for small cell lung cancer include:

• Smoking cigarettes, cigars, or pipes now or in the past.
• Being exposed to secondhand smoke.
• Being exposed to asbestos or radon.

Possible signs of small cell lung cancer include coughing, chest pain, and shortness of breath.

These and other symptoms may be caused by small cell lung cancer. Other conditions may cause the same symptoms. A doctor should be consulted if any of the following problems occur:

• A cough that doesn’t go away.
• Shortness of breath.
• Chest pain that doesn’t go away.
• Wheezing.
• Coughing up blood.
• Hoarseness.
• Swelling of the face and neck.
• Loss of appetite.
• Weight loss for no known reason.
• Unusual tiredness.