Cancer is a general term for many diseases in which abnormal cells divide without control. A cell is an individual unit that makes up the tissues of the body.

Normally, cells grow and divide in a controlled way to produce more cells when the body needs them to keep healthy. When cells become old or damaged, they die and are replaced with new cells. Sometimes, however, this orderly process goes wrong. The genetic material (DNA) of a cell can become damaged or changed, producing mutations that affect normal cell growth and division. When this happens, cells do not die when they should, and new cells form when the body does not need them.

The extra cells may form a solid mass of tissue called a tumor. Tumors can press on other parts of the body, and they develop their own blood supply, which robs the body of nutrients it needs because these are being used by the tumor. When abnormal cells do not form a tumor, they can crowd out normal cells and interfere with body functions.

Cancer cells can spread from the place where the disease started to many parts of the body through the blood and lymphatic systems. There are more than 100 different types of cancer. Most cancers are named for the organ or type of cell in which they start - the primary site.

For example, cancer that begins in the colon is called colon cancer; cancer that begins in basal cells of the skin is called basal cell carcinoma.  

Scientists have learned a great deal about treating cancer over many decades of research, and treatments have become much more effective. Today, most people with cancer are treated with a combination of therapies. Treatment choices depend on many factors, including the severity, or stage, of the disease, the patient’s age and general health, and the parts of the body that are affected if the cancer has spread (metastasized) from its primary site.