Cancer is a group of diseases characterized by an uncontrolled growth of
abnormal cells. If the spread of these abnormal cells is not controlled, cancer
can cause death. Most cancers take the form of tumors, although not all tumors
are cancers. A tumor is simply a mass of new tissue that serves no
physiological purpose. It can be benign, like a wart, or malignant, like cancer.
Benign tumors are made up of cells similar to the surrounding normal cells and
are enclosed in a membrane that prevents them from penetrating neighboring
tissues. They are dangerous only if their physical presence interferes with
bodily functions. A malignant tumor, or cancer, is capable of invading
surrounding structures, including blood vessels, the lymph system and nerves.
It can also spread to distant sites by the blood and lymphatic circulation and
so can produce invasive tumors in almost any part of the body.
In 1997, an estimated 1,359,150 people in the United...