A tumor is an abnormal growth of body tissue. Tumors can be cancerous (malignant) or noncancerous (benign).
In general, tumors occur when cells divide excessively in the body. Typically, cell division is strictly controlled. New cells are created to replace older ones or to perform new functions. Cells that are damaged or no longer needed die to make room for healthy replacements.
If the balance of cell division and death is disturbed, a tumor may form.
Problems with the body's immune system can lead to tumors. Tobacco causes more deaths from cancer than any other environmental substance. Other causes include:
Types of tumors known to be caused by viruses are:
Some tumors are more common in one gender than the other. Some are more common among children or the elderly. Others are related to diet, environment, and family history.
Moscow JA, Cowan KH. Biology of cancer. In: Goldman L, Ausiello D, eds. Cecil Medicine. 23rd ed. Philadelphia, Pa: Saunders Elsevier;2007:chap 187.
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