A tumor is an abnormal growth of body tissue. Tumors can be
cancerous (malignant) or noncancerous (benign). Causes,
incidence, and risk factors 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: - Benzene and
other chemicals and toxins - Drinking too much 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 Types of tumors
known to be caused by viruses are: Some tumors are more common
in one gender than the other. Some are more comm