¿What is Cancer?
Cancer is a term used for diseases in which abnormal cells divide without control and are able to invade other tissues. Cancer cells can spread to other parts of the body through the blood and lymph systems.
Cancer is not just one disease but many diseases. There are more than 100 different types of cancer. Most cancers are named for the organ or type of cell in which they start - for example, cancer that begins in the colon is called colon cancer; cancer that begins in basal cells of the skin is called basal cell carcinoma.
Cancer types can be grouped into broader categories. The main categories of cancer include:
- Carcinoma - cancer that begins in the skin or in tissues that line or cover internal organs.
- Sarcoma - cancer that begins in bone, cartilage, fat, muscle, blood vessels, or other connective or supportive tissue.
- Leukemia - cancer that starts in blood-forming tissue such as the bone marrow and causes large numbers of abnormal blood cells to be produced and enter the blood.
- Lymphoma and myeloma - cancers that begin in the cells of the immune system.
- Central nervous system cancers - cancers that begin in the tissues of the brain and spinal cord.
Origins of Cancer
All cancers begin in cells, the body's basic unit of life. To understand cancer, it's helpful to know what happens when normal cells become cancer cells.
The body is made up of many types of cells. These cells grow and divide in a controlled way to produce more cells as they are needed to keep the body healthy. When cells become old or damaged, they die and are replaced with new cells.
However, sometimes this orderly process goes wrong. The genetic material (DNA) of a cell can become damaged or changed, producing mutations that affect normal cell growth and division. When this happens, cells do not die when they should and new cells form when the body does not need them. The extra cells may form a mass of tissue called a tumor.
Not all tumors are cancerous; tumors can be benign or malignant.
- Benign tumors aren't cancerous. They can often be removed, and, in most cases, they do not come back. Cells in benign tumors do not spread to other parts of the body.
- Malignant tumors are cancerous. Cells in these tumors can invade nearby tissues and spread to other parts of the body. The spread of cancer from one part of the body to another is called metastasis.
Some cancers do not form tumors. For example, leukemia is a cancer of the bone marrow and blood.
Understanding Cancer
Cancer begins in cells, the building blocks that form tissues. Tissues make up the organs of the body.
Normally, cells grow and divide to form new cells as the body needs them. When cells grow old, they die, and new cells take their place.
Sometimes, this orderly process goes wrong. New cells form when the body does not need them, and old cells do not die when they should. These extra cells can form a mass of tissue called a growth or tumor.
Tumors can be benign or malignant:
- Benign tumors are rarely life-threatening.
- Generally, benign tumors can be removed, and they usually do not grow back.
- Cells from benign tumors do not invade the tissues around them.
- Cells from benign tumors do not spread to other parts of the body.
- Malignant tumors are cancer:
- Malignant tumors are generally more serious than benign tumors. They may be life-threatening.
- Malignant tumors often can be removed, but sometimes they grow back.
- Cells from malignant tumors can invade and damage nearby tissues and organs.
- Cells from malignant tumors can spread (metastasize) to other parts of the body.
- Cancer cells spread by breaking away from the original (primary) tumor and entering the bloodstream or lymphatic system. The cells can invade other organs, forming new tumors that damage these organs. The spread of cancer is called metastasis.
Most cancers are named for where they start. For example, lung cancer starts in the lung, and breast cancer starts in the breast. Lymphoma is cancer that starts in the lymphatic system. And leukemia is cancer that starts in white blood cells (leukocytes).
When cancer spreads and forms a new tumor in another part of the body, the new tumor has the same kind of abnormal cells and the same name as the primary tumor. For example, if prostate cancer spreads to the bones, the cancer cells in the bones are actually prostate cancer cells. The disease is metastatic prostate cancer, not bone cancer. For that reason, it is treated as prostate cancer, not bone cancer. Doctors sometimes call the new tumor "distant" or metastatic disease.
Risk Factors
Doctors often cannot explain why one person develops cancer and another does not. But research shows that certain risk factors increase the chance that a person will develop cancer. These are the most common risk factors for cancer:
- Growing older
- Tobacco
- Sunlight
- Ionizing radiation
- Certain chemicals and other substances
- Some viruses and bacteria
- Certain hormones
- Family history of cancer
- Alcohol
- Poor diet, lack of physical activity, or being overweight
Many of these risk factors can be avoided. Others, such as family history, cannot be avoided. People can help protect themselves by staying away from known risk factors whenever possible.
If you think you may be at risk for cancer, you should discuss this concern with your doctor. You may want to ask about reducing your risk and about a schedule for checkups.
Over time, several factors may act together to cause normal cells to become cancerous.
When thinking about your risk of getting cancer, these are some things to keep in mind:
- Not everything causes cancer.
- Cancer is not caused by an injury, such as a bump or bruise.
- Cancer is not contagious. Although being infected with certain viruses or bacteria may increase the risk of some types of cancer, no one can "catch" cancer from another person.
- Having one or more risk factors does not mean that you will get cancer. Most people who have risk factors never develop cancer.
- Some people are more sensitive than others to the known risk factors.
The sections below have more detailed information about the most common risk factors for cancer. You also may want to read the NCI booklet Cancer and the Environment.
Growing Older
The most important risk factor for cancer is growing older. Most cancers occur in people over the age of 65. But people of all ages, including children, can get cancer, too.
Tobacco
Tobacco use is the most preventable cause of death. Each year, more than 180,000 Americans die from cancer that is related to tobacco use.
Using tobacco products or regularly being around tobacco smoke (environmental or secondhand smoke) increases the risk of cancer.
Smokers are more likely than nonsmokers to develop cancer of the lung, larynx (voice box), mouth, esophagus, bladder, kidney, throat, stomach, pancreas, or cervix. They also are more likely to develop acute myeloid leukemia (cancer that starts in blood cells).
People who use smokeless tobacco (snuff or chewing tobacco) are at increased risk of cancer of the mouth.
Sunlight
Ultraviolet (UV) radiation comes from the sun, sunlamps, and tanning booths. It causes early aging of the skin and skin damage that can lead to skin cancer.
Doctors encourage people of all ages to limit their time in the sun and to avoid other sources of UV radiation:
- It is best to avoid the midday sun (from mid-morning to late afternoon) whenever possible. You also should protect yourself from UV radiation reflected by sand, water, snow, and ice. UV radiation can penetrate light clothing, windshields, and windows.
- Wear long sleeves, long pants, a hat with a wide brim, and sunglasses with lenses that absorb UV.
- Use sunscreen. Sunscreen may help prevent skin cancer, especially sunscreen with a sun protection factor (SPF) of at least 15. But sunscreens cannot replace avoiding the sun and wearing clothing to protect the skin.
Stay away from sunlamps and tanning booths. They are no safer than sunlight.
Protect yourself from the sun. |
Ionizing Radiation
Ionizing radiation can cause cell damage that leads to cancer. This kind of radiation comes from rays that enter the Earth's atmosphere from outer space, radioactive fallout, radon gas, x-rays, and other sources.
Radioactive fallout can come from accidents at nuclear power plants or from the production, testing, or use of atomic weapons. People exposed to fallout may have an increased risk of cancer, especially leukemia and cancers of the thyroid, breast, lung, and stomach.
Radon is a radioactive gas that you cannot see, smell, or taste. It forms in soil and rocks. People who work in mines may be exposed to radon. In some parts of the country, radon is found in houses. People exposed to radon are at increased risk of lung cancer.
Medical procedures are a common source of radiation:
- Doctors use radiation (low-dose x-rays) to take pictures of the inside of the body. These pictures help to diagnose broken bones and other problems.
- Doctors use radiation therapy (high-dose radiation from large machines or from radioactive substances) to treat cancer.
The risk of cancer from low-dose x-rays is extremely small. The risk from radiation therapy is slightly higher. For both, the benefit nearly always outweighs the small risk.
You should talk with your doctor if you are concerned that you may be at risk for cancer due to radiation.
If you live in a part of the country that has radon, you may wish to test your home for high levels of the gas. The home radon test is easy to use and inexpensive. Most hardware stores sell the test kit.
You should talk with your doctor or dentist about the need for each x-ray. You should also ask about shields to protect parts of the body that are not in the picture.
Cancer patients may want to talk with their doctor about how radiation treatment could increase their risk of a second cancer later on.
Certain Chemicals and Other Substances
People who have certain jobs (such as painters, construction workers, and those in the chemical industry) have an increased risk of cancer. Many studies have shown that exposure to asbestos, benzene, benzidine, cadmium, nickel, or vinyl chloride in the workplace can cause cancer.
Follow instructions and safety tips to avoid or reduce contact with harmful substances both at work and at home. Although the risk is highest for workers with years of exposure, it makes sense to be careful at home when handling pesticides, used engine oil, paint, solvents, and other chemicals.
Some Viruses and Bacteria
Being infected with certain viruses or bacteria may increase the risk of developing cancer:
Do not have unprotected sex or share needles. You can get an HPV infection by having sex with someone who is infected. You can get hepatitis B, hepatitis C, or HIV infection from having unprotected sex or sharing needles with someone who is infected.
You may want to consider getting the vaccine that prevents hepatitis B infection. Health care workers and others who come into contact with other people's blood should ask their doctor about this vaccine.
If you think you may be at risk for HIV or hepatitis infection, ask your doctor about being tested. These infections may not cause symptoms, but blood tests can show whether the virus is present. If so, the doctor may suggest treatment. Also, the doctor can tell you how to avoid infecting other people.
If you have stomach problems, see a doctor. Infection with H. pylori can be detected and treated.
Certain Hormones
Doctors may recommend hormones (estrogen alone or estrogen along with progestin) to help control problems (such as hot flashes, vaginal dryness, and thinning bones) that may occur during menopause. However, studies show that menopausal hormone therapy can cause serious side effects. Hormones may increase the risk of breast cancer, heart attack, stroke, or blood clots.
A woman considering menopausal hormone therapy should discuss the possible risks and benefits with her doctor.
Diethylstilbestrol (DES), a form of estrogen, was given to some pregnant women in the United States between about 1940 and 1971. Women who took DES during pregnancy may have a slightly higher risk of developing breast cancer. Their daughters have an increased risk of developing a rare type of cancer of the cervix. The possible effects on their sons are under study.
Women who believe they took DES and daughters who may have been exposed to DES before birth should talk with their doctor about having checkups.
Family History of Cancer
Most cancers develop because of changes (mutations) in genes. A normal cell may become a cancer cell after a series of gene changes occur. Tobacco use, certain viruses, or other factors in a person's lifestyle or environment can cause such changes in certain types of cells.
Some gene changes that increase the risk of cancer are passed from parent to child. These changes are present at birth in all cells of the body.
It is uncommon for cancer to run in a family. However, certain types of cancer do occur more often in some families than in the rest of the population. For example, melanoma and cancers of the breast, ovary, prostate, and colon sometimes run in families. Several cases of the same cancer type in a family may be linked to inherited gene changes, which may increase the chance of developing cancers. However, environmental factors may also be involved. Most of the time, multiple cases of cancer in a family are just a matter of chance.
If you think you may have a pattern of a certain type of cancer in your family, you may want to talk to your doctor. Your doctor may suggest ways to try to reduce your risk of cancer. Your doctor also may suggest exams that can detect cancer early.
You may want to ask your doctor about genetic testing. These tests can check for certain inherited gene changes that increase the chance of developing cancer. But inheriting a gene change does not mean that you will definitely develop cancer. It means that you have an increased chance of developing the disease.
Alcohol
Having more than two drinks each day for many years may increase the chance of developing cancers of the mouth, throat, esophagus, larynx, liver, and breast. The risk increases with the amount of alcohol that a person drinks. For most of these cancers, the risk is higher for a drinker who uses tobacco.
Doctors advise people who drink to do so in moderation. Drinking in moderation means no more than one drink per day for women and no more than two drinks per day for men.
Poor Diet, Lack of Physical Activity, or Being Overweight
People who have a poor diet, do not have enough physical activity, or are overweight may be at increased risk of several types of cancer. For example, studies suggest that people whose diet is high in fat have an increased risk of cancers of the colon, uterus, and prostate. Lack of physical activity and being overweight are risk factors for cancers of the breast, colon, esophagus, kidney, and uterus.
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Choose a diet rich in fruits and vegetables. |
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