Cancer is the uncontrolled growth of abnormal cells in the body. Cancerous cells are also called malignant cells.

Carcinoma; Malignant tumor

Cells are the building blocks of living things.

Cancer grows out of normal cells in the body. Normal cells multiply when the body needs them, and die when the body doesn't need them. Cancer appears to occur when the growth of cells in the body is out of control and cells divide too quickly. It can also occur when cells forget how to die.

There are many different kinds of cancers. Cancer can develop in almost any organ or tissue, such as the lung, colon, breast, skin, bones, or nerve tissue.

There are many causes of cancers, including:

• Benzene and other chemicals
• Drinking excess alcohol
• Environmental toxins, such as certain poisonous mushrooms and a type of poison that can grow on peanut plants (aflatoxins)
• Excessive sunlight exposure
• Genetic problems
• Obesity
• Radiation
• Viruses

However, the cause of many cancers remains unknown.

The most common cause of cancer-related death is lung cancer.

The three most common cancers in men in the United States are:

• Prostate cancer
• Lung cancer
• Colon cancer

In women in the United States, the three most common cancers are:

• Breast cancer
• Colon cancer
• Lung cancer

Some cancers are more common in certain parts of the world. For example, in Japan, there are many cases of stomach cancer, but in the United States, this type of cancer is pretty rare. Differences in diet may play a role.

Some other types of cancers include:

• Brain cancer
• Cervical cancer
• Hodgkin's lymphoma
• Kidney cancer
• Leukemia
• Liver cancer
• Non-Hodgkin's lymphoma
• Ovarian cancer
• Skin cancer
• Testicular cancer
• Thyroid cancer
• Uterine cancer

Review Date: 08/14/2010
Reviewed By: David C. Dugdale, III, MD, Professor of Medicine, Division of General Medicine, Department of Medicine, University of Washington School of Medicine. Also reviewed by David Zieve, MD, MHA, Medical Director, A.D.A.M., Inc.

A.D.A.M., Inc. is accredited by URAC, also known as the American Accreditation HealthCare Commission (www.urac.org)