Cancer is a disease in which cells of an organ or tissue in the body become
abnormal, failing to respond to normal growth control mechanisms and continuing
to grow and multiply out of control.
When cells grow out of control they usually form a mass, called a tumor.
Some tumors grow and enlarge only at the site where they begin and these are
referred to as benign tumors. Other tumors not only enlarge locally,
but also have the potential to invade and destroy the normal tissue around them
and to spread to distant parts of the body. These tumors are called malignant
tumors or cancers.
Distant spread of cancer occurs when malignant cells become detached from the
original (primary) tumor, get carried to other parts of the body through the
blood or lymphatic vessels, and establish themselves in the new site as an independent
(secondary) cancer. A tumor that has spread in this manner is said to have
metastasized. The secondary tumor (or tumors) is called a metastasis
(or metastases).
Since cancer may develop in any tissue of any organ, there are many different
types of cancer. About 38% of women and 41% of men will develop cancer at some
point during their life.