Cancer is a term for diseases in which abnormal cells divide without control and can invade other tissues. Cancer cells can spread to other parts of the body through the blood and lymph systems.

Cancer is not just one disease but many diseases. There are more than 100 different types of cancer. The main categories of cancer include:

• Carcinoma - cancer that begins in the skin or in tissues that line or cover internal organs.
• Sarcoma - cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.
• Leukemia - cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood.
• Lymphoma and myeloma - cancers that begin in the cells of the immune system.
• Central nervous system cancers - cancers that begin in the tissues of the brain and spinal cord.

For definitions of other cancer-related terms, see NCI's Dictionary of Cancer Terms.

Source: National Cancer Institute