Cancer, Causes
The information provided below
has been modified from that furnished by the National Institutes of Health and
the National Cancer Institute of the United States of America.
What is cancer?
Cancer is a group of more than 100 different diseases. Cancer occurs when cells
become abnormal and keep dividing and forming more cells without control or order.
All organs of the body are made up of cells. Normally, cells divide to produce
more cells only when the body needs them. This orderly process helps keep us healthy.
If cells keep dividing when new cells are not needed, a mass of tissue forms.
This mass of extra tissue, called a growth or tumor, can be benign or malignant.
Benign tumors are not cancer. They can usually be removed and, in most cases,
they do not come back. Most important, cells from benign tumors do not spread
to other parts of the body. Benign tumors are rarely a threat to life.
Malignant tumors are cancer. Cancer cells can invade and damage nearby tissues
and organs. Also, cancer cells can break away from a malignant tumor and enter
the bloodstream or the lymphatic system. This is how cancer spreads from the original
(primary) tumor to form new tumors in other parts of the body. The spread of cancer
is called metastasis.
Most cancers are named for the type of cell or the organ in which they begin.
When cancer spreads, the new tumor has the same kind of abnormal cells and the
same name as the primary tumor. For example, if lung cancer spreads to the liver, the
cancer cells in the liver are lung cancer cells. The disease is called metastatic
lung cancer (not liver cancer).
What causes cancer, and how can it be prevented?
The number of new cases of cancer in the United States is increasing each year.
People of all ages get cancer, but nearly all types are more common in middle-aged
and elderly people than in young people. Skin cancer is the most common type of
cancer for both men and women. The next most common type among men is prostate cancer; among women, it is breast cancer. Lung cancer, however,
is the leading cause of death from cancer for both men and women in the United
States. Brain cancer and leukemia are the most common cancers
in children and young adults.
The more we can learn about what causes cancer, the more likely we are to find
ways to prevent it. Scientists study patterns of cancer in the population to look
for factors that affect the risk of developing this disease. In the laboratory,
they explore possible causes of cancer and try to determine what actually happens
when normal cells become cancerous.
Our current understanding of the causes of cancer is incomplete, but it is clear
that cancer is not caused by an injury, such as a bump or bruise. And although
being infected with certain viruses may increase the risk of some types of cancer,
cancer is not contagious. No one can "catch" cancer from another person.
Cancer develops gradually as a result of a complex mix of factors related to environment,
lifestyle, and heredity. Scientists have identified many risk factors that increase
the chance of getting cancer. They estimate that about 80 percent of all cancers
are related to the use of tobacco products, to what we eat and drink, or, to a
lesser extent, to exposure to radiation or cancer-causing agents (carcinogens)
in the environment and the workplace. Some people are more sensitive than others
to factors that can cause cancer.
Many risk factors can be avoided. Others, such as inherited risk factors, are
unavoidable. It is helpful to be aware of them, but it is also important to keep
in mind that not everyone with a particular risk factor for cancer actually develops
the disease. In fact, most do not. People at risk can help protect themselves
by avoiding risk factors where possible and by getting regular checkups, so that
if cancer develops, it is likely to be found early.
These are some of the factors that are known to increase the risk of cancer:
TOBACCO Tobacco causes cancer. In fact, smoking tobacco, using "smokeless" tobacco,
and being regularly exposed to environmental tobacco smoke without actually smoking
are responsible for one-third of all cancer deaths in the United States each year.
Tobacco use is the most preventable cause of death in this country.
Smoking accounts for more than 85 percent of all lung cancer deaths. If you smoke,
your risk of getting lung cancer is affected by the number and types of cigarettes
you smoke and how long you have been smoking. Overall, for those who smoke one
pack a day, the chance of getting lung cancer is about 10 times greater than for
nonsmokers. Smokers are also more likely than nonsmokers to develop several other
types of cancer (such as oral cancer and cancers of the larynx,
esophagus, pancreas, bladder, kidney, and cervix). The risk of cancer begins to
decrease when a smoker quits, and the risk continues to decline gradually each
year after quitting.
The use of smokeless tobacco (chewing tobacco and snuff) causes cancer of the
mouth and throat. Precancerous conditions, or tissue changes that may lead to
cancer, begin to go away after a person stops using smokeless tobacco.
Exposure to environmental tobacco smoke, also called involuntary smoking, increases
the risk of lung cancer for nonsmokers. The risk goes up 30 percent or more for
a nonsmoking spouse of a person who smokes. Involuntary smoking causes about 3,000
lung cancer deaths in this country each year.
If you use tobacco in any form and you need help quitting, talk with your doctor
or dentist, or join a smoking cessation group sponsored by a local hospital or
voluntary organization. For information on such groups or other programs, call
the Cancer Information Service (1-800-422-6237) or the American Cancer Society
(1-800-227-2345).
DIET
Your choice of foods may affect your chance of developing cancer. Evidence points
to a link between a high-fat diet and certain cancers, such as cancer of the breast,
colon, uterus, and prostate. Being seriously overweight appears to be linked to
increased rates of cancer of the prostate, pancreas, uterus, colon, and ovary,
and to breast cancer in older women. On the other hand, studies suggest that foods
containing fiber and certain nutrients help protect
us against some types of cancer.
You may be able to reduce your cancer risk by making some simple food choices.
Try to have a varied, well-balanced diet that includes generous amounts of foods
that are high in fiber, vitamins, and minerals. At the same time, try to cut down
on fatty foods. You should eat five servings of fruits and vegetables each day,
choose more whole-grain breads and cereals, and cut down on eggs, high-fat meat,
high-fat dairy products (such as whole milk, butter, and most cheeses), salad
dressings, margarine, and cooking oils.
SUNLIGHT
Ultraviolet radiation from the sun and from other sources (such as sunlamps and
tanning booths) damages the skin and can cause skin cancer. Repeated exposure to ultraviolet
radiation increases the risk of skin cancer, especially if you have fair skin
or freckle easily. The sun's ultraviolet rays are strongest during the summer
from about 11 a.m. to about 3 p.m. (daylight savings time). The risk is greatest
at this time, when the sun is high overhead and shadows are short. As a rule,
it is best to avoid the sun when your shadow is shorter than you are.
Protective clothing, such as a hat and long sleeves, can help block the sun's
harmful rays. You can also use sunscreens to help protect yourself. Sunscreens
are rated in strength according to their SPF (sun protection factor), which ranges
from 2 to 30 and higher. Those rated 15 to 30 block most of the sun's harmful
rays.
ALCOHOL
Drinking large amounts of alcohol increases the risk of cancer of the mouth, throat,
esophagus, and larynx. (People who smoke cigarettes and drink alcohol have an
especially high risk of getting these cancers). Alcohol can damage the liver and
increase the risk of liver cancer. Some studies suggest that drinking alcohol
also increases the risk of breast cancer. So if you drink at all,
do so in moderation, not more than one or two drinks a day.
RADIATION
Exposure to large doses of radiation from medical x-rays can increase the risk
of cancer. X-rays used for diagnosis expose you to very little radiation and the
benefits nearly always outweigh the risks. However, repeated exposure can be harmful,
so it is a good idea to talk with your doctor or dentist about the need for each
x-ray and ask about the use of shields to protect other parts of your body.
Before 1950, x-rays were used to treat noncancerous conditions (such as an enlarged
thymus, enlarged tonsils and adenoids, ringworm of the scalp, and acne) in children and young adults. People
who have received radiation to the head and neck have a higher-than-average risk
of developing thyroid cancer years later. People with
a history of such treatments should report it to their doctor and should have
a careful exam of the neck every 1 or 2 years.
CHEMICALS AND OTHER SUBSTANCES IN THE WORKPLACE
Being exposed to substances such as metals, dust, chemicals, or pesticides at
work can increase the risk of cancer. Asbestos, nickel, cadmium, uranium, radon,
vinyl chloride, benzidene, and benzene are well-known examples of carcinogens
in the workplace. These may act alone or along with another carcinogen, such as
cigarette smoke. For example, inhaling asbestos fibers increases the risk of lung
diseases, including cancer, and the cancer risk is especially high for asbestos
workers who smoke. It is important to follow work and safety rules to avoid contact
with dangerous materials.
HORMONE REPLACEMENT THERAPY
Many women use estrogen therapy to control the hot flashes, vaginal dryness, and
osteoporosis (thinning of the bones)
that can occur during menopause. However, studies show that
estrogen uses increases the risk of cancer of the uterus. Other studies suggest
an increased risk of breast cancer among women who have used high doses of estrogen
or have used estrogen for a long time. At the same time, taking estrogen may reduce
the risk of heart disease and osteoporosis.
The risk of uterine cancer appears to be less when progesterone is used with estrogen
than when estrogen is used alone. But some scientists are concerned that the addition
of progesterone may also increase the risk of breast cancer.
Researchers are still studying and finding new information about the risks and
benefits of taking replacement hormones. A woman considering hormone replacement therapy should discuss
these issues with her doctor.
DIETHYLSTILBESTROL (DES)
DES is a form of estrogen that doctors prescribed from the early 1940s until 1971
to try to prevent miscarriage. In some daughters of women
who were given DES during pregnancy, the uterus, vagina, and cervix do not develop
normally. DES-exposed daughters also have an increased chance of developing abnormal
cells (dysplasia) in the cervix and vagina. In addition, a rare type of vaginal
and cervical cancer has been found in a small number of DES-exposed daughters.
Women who took DES during pregnancy may have a slightly increased risk of developing
breast cancer. DES-exposed mothers and daughters should inform their doctor about
this exposure. DES daughters should have regular special pelvic exams by a doctor
familiar with conditions related to DES.
Exposure to DES before birth does not appear to increase the risk of cancer in
DES-exposed sons. However, reproductive and urinary system problems may occur.
These men should inform the doctor and have regular medical checkups.
CLOSE RELATIVES WITH CERTAIN TYPES OF CANCER
A small number of cancers (including melanoma and cancers of the breast, ovary,
and colon) tend to occur more often in some families than in the rest of the population.
It is not always clear whether a pattern of cancer in a family is due to heredity,
factors in the family's environment, or chance. Still, if close relatives have
been affected by cancer, it is important to let your doctor know this and then
follow the doctor's advice about cancer prevention and checkups to detect problems
early.
Cancer Causes At A Glance
- Cancer is a group of more
than 100 different diseases.
- Benign tumors are not cancer.
Malignant tumors are cancer.
- Most cancers are named
for the type of cell or the organ in which they begin.
- When cancer spreads (metastasizes),
the new tumor has the same name as the original (primary) tumor.
- Skin cancer is the most
common type of cancer for both men and women.
- The second most common
cancer in men is prostate cancer, in women it is breast cancer.
- Lung cancer is the leading
cause of death from cancer for both men and women in the U.S.
- Cancer is NOT contagious.
- Risk factors have been
identified for most cancers.
© 1996-2001 MedicineNet,
Inc.
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