Cancer develops when cells in a part of the body begin to grow out of control.
Although there are many kinds of cancer, they all start because of out-of-control
growth of abnormal cells.
Normal body cells grow, divide, and die in an
orderly fashion. During the early years of a person's life, normal cells divide
more rapidly until the person becomes an adult. After that, cells in most parts
of the body divide only to replace worn-out or dying cells and to repair injuries.
Because cancer cells continue to grow and divide, they are different from
normal cells. Instead of dying, they outlive normal cells and continue to form
new abnormal cells.
Cancer cells often travel to other parts of the body
where they begin to grow and replace normal tissue. This process, called metastasis,
occurs as the cancer cells get into the bloodstream or lymph vessels of our body.
When cells from a cancer like melanoma skin cancer spread to another organ like
the liver, the cancer is still called melanoma, not liver cancer.
cells develop because of damage to DNA. This substance is in every cell and directs
all its activities. Most of the time when DNA becomes damaged the body is able
to repair it. In cancer cells, the damaged DNA is not repaired. People can inherit
damaged DNA, which accounts for inherited cancers. Many times though, a personís
DNA becomes damaged by exposure to something in the environment, like smoking.
Cancer usually forms as a tumor. Some cancers, like leukemia, do not form tumors.
Instead, these cancer cells involve the blood and blood-forming organs and circulate
through other tissues where they grow.
Not all tumors are cancerous. Benign
(noncancerous) tumors do not spread to other parts of the body (metastasize) and,
with very rare exceptions, are not life threatening.
Different types of
cancer can behave very differently. For example, lung cancer and breast cancer
are very different diseases. They grow at different rates and respond to different
treatments. That is why people with cancer need treatment that is aimed at their
particular kind cancer.
Cancer is the leading cause of death in people
under age 85 the United States. Nearly half of all men and a little over one third
of all women in the US will develop cancer during their lifetimes. Today, millions
of people are living with cancer or have had cancer. The risk of developing most
types of cancer can be reduced by changes in a person's lifestyle, for example,
by quitting smoking and eating a better diet. The sooner a cancer is found and
treatment begins, the better are the chances for living for many years.