Cancer is a group of many related diseases. Most forms of cancer evolve from out-of-control growth and spread 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, normal cells of most tissues divide only to replace
worn-out or dying cells and to repair injuries.
Cancer cells, however, continue to grow and divide. Cancer cells do not die off
in a programmed way. They can spread to other parts of the body. These cells
accumulate and form tumors (lumps) that may compress, invade, and destroy normal
tissue. If cells break away from such a tumor, they can travel through the bloodstream,
or the lymph system to other areas of the body. There, they may settle and form "colony" tumors
or "daughter" tumors. In their new location, the cancer cells continue
growing. The spread of a tumor to a new site is called metastasis. When cancer
spreads, though, it is still named after the part of the body where it started.
For example, if prostate cancer spreads to the bones, it is still prostate cancer,
and if breast cancer spreads to the lungs it is still called breast cancer.
Leukemia, a form of cancer, does not usually form a tumor. Instead, these cancer
cells involve the blood and blood-forming organs (bone marrow, lymphatic system,
and spleen), and circulate through other tissues where they can accumulate.
It is important to realize that not all tumors are cancerous. Benign (noncancerous)
tumors, for example, benign brain tumors, do not metastasize and, with very rare
exceptions, are not life-threatening.
Cancer is classified by the part of the body in which it began, and by its appearance
under a microscope. Different types of cancer vary in their rates of growth,
patterns of spread, and responses to different types of treatment. That's why
people with cancer need treatment that is aimed at their specific form of the
disease.
In America, half of all men and one-third of all women will develop cancer during
their lifetimes. Today, millions of people are living with cancer or have been
cured of the disease. The risk of developing most types of cancer can be reduced
by changes in a person’s lifestyle, for example, by quitting smoking or
eating a better diet. The sooner a cancer is found, and the sooner treatment
begins, the better a patient’s chances are of a cure.
A risk factor is anything that increases a person's
chance of developing a disease such as cancer. Different cancers have different
risk factors. For example, smoking is a risk factor for cancers of the
lungs, mouth, throat, larynx, bladder, and several other organs. It is
important to remember, however, that these factors increase a person's
risk but do not always "cause" the disease. Many people with
one or more risk factors never develop cancer, while others with this disease
have no known risk factors. It is important, however, to know about risk
factors so that appropriate action can be taken, such as changing a health
behavior or being monitored closely for a potential cancer.
All cancers caused by cigarette smoking and heavy use of alcohol could be prevented
completely. The ACS estimates that in 1998 about 175,000 cancer deaths are expected
to be caused by tobacco use and an additional 19,000 cancer deaths are related
to excessive alcohol use, frequently in combination with tobacco use.
Many cancers that are related to dietary factors could also be prevented. Scientific
evidence suggests that up to one-third of the 564,800 cancer deaths expected
to occur in the US this year are related to nutrition.
In addition, many of the one million skin cancers that are expected to be diagnosed
in 1998 could have been prevented by protection from the sun's rays.
Reprint from The American Cancer Society, edited by
Dr. James Forsythe
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