To be able to control, treat or prevent cancer we have to understand what causes it. Research has showed that there is no one single cause for cancer. Cancer is the result of interaction of many genetic or acquired factors or even unknown causes that produce cancer.

Cancer begins with damage (mutations) in the DNA. DNA is like a set of instructions for the cells, telling them how to grow and divide. Normal cells often develop mutations in their DNA during the course of their division, but they have the ability to repair most of these or, if they can't make these repairs, the cells often die. However, certain mutations aren't repaired, causing the cells to grow and become cancerous. Mutations also cause cancer cells to live beyond a normal cell life span. This causes the cancerous cells to accumulate.

A number of changes need to take place within cells to develop cancer:

• Initiator causes a genetic mutation – The initial genetic mutation is just the beginning of the process by which cancer develops. Sometimes this initial genetic mutation can exist since birth. Other times a genetic mutation is caused by factors within the body, such as hormones, viruses and chronic inflammation. Genetic mutations can also be caused by forces outside the body, such as ultraviolet (UV) light from the sun or cancer-causing chemicals (carcinogens) in the environment.
• Promoter cause rapid cell growth – Promoters take advantage of genetic mutations created by initiators. Promoters cause cells to divide rapidly. This could lead to a tumor. Promoters could be inherited, or could come from either inside the body or outside the body.
• Progressor cause cancer to spread – Without a progressor a tumor may remain benign and localized. Progressors make cancers more aggressive locally and make them more likely to spread. Like initiators and promoters, progressors could be inherited or they could come from environmental sources.

Genetic makeup of the body, lifestyle choices and environment can all set the stage for cancer or help expedite the process once it's started. If a genetic mutation that may lead to cancer is inherited, one may be more likely than others to develop cancer if exposed to a certain cancer-causing substance. The genetic mutation begins the cancer process, and the cancer-causing substance furthers the cancer development. Likewise, smokers who work with asbestos are more likely to develop lung cancer than smokers who don't work with asbestos because both these carcinogens contribute in cancer development.

Cancers seen in childhood often occur or begin in the stem cells, which are progenitor cells capable of producing other types of specialized cells that the body needs. A sporadic cell change (occurs by chance) or mutation usually causes childhood cancer. In adults, the type of cell that becomes cancerous is usually an "epithelial" cell, which is one of the cells that line the body cavity, including the surfaces of organs, glands, or body structures, and skin. Cancer in adults usually occurs from environmental exposures of these cells to various agents over time.

The causes of cancer can be understood if the risk factors for cancer are outlined. Some cancers, particularly in adults, have been associated with specific risk factors. A risk factor is anything that may increase a person's chance of developing a disease. It does not necessarily cause the disease, but may make the body less resistant to it. Persons who have an increased risk of developing cancer can help to protect themselves by scheduling regular screenings and check-ups with their physician. Avoiding certain risk factors (like smoking) certainly decreases the risk of individual risk to cancer.

Major Causes

The following risk factors and mechanisms have been proposed as contributing to the development of cancer:

Lifestyle Factors: Lifestyle and environmental factors such as smoking, high-fat diet, exposure to ultraviolet light (UV radiation from the sun), or exposure to chemicals (cancer-causing substances) in the work place over long periods of time may be risk factors for some adult cancers. Most children with cancer, however, are too young to have been exposed to these lifestyle factors for any extended time.

Genetic Factors: Family history, inheritance, and genetics may play an important role in some adult and childhood cancers. It is possible for cancer of varying forms to be present in a family and some gene alterations are inherited. However, this does not necessary mean that the person will develop cancer. It indicates that the chance of developing cancer increases. It is unknown in these circumstances if the disease is caused by a genetic mutation, other factors, or simply coincidence.

The discovery of certain types of genes that contribute to cancer has been an extremely important development for cancer research. Over 90 percent of cancers are observed to have some type of genetic alteration. A small percentage (5 percent to 10 percent) of these alterations are inherited, while the rest are sporadic, which means they occur by chance or occur from environmental exposures (usually over many years). There are three main types of genes that can affect cell growth, and are altered (mutated) in certain types of cancers. These are:

• Oncogenes – These genes regulate the normal growth of cells. Scientists commonly describe oncogenes as similar to a cancer "switch" that most people have in their bodies. What "flips the switch" to make these oncogenes suddenly become unable to control the normal growth of cells and allowing abnormal cancer cells to begin to grow, is unknown.
• Tumor Suppressor Genes – These genes are able to recognize abnormal growth and reproduction of damaged cells, or cancer cells, and can interrupt their reproduction until the defect is corrected. If the tumor suppressor genes are mutated, however, and they do not function properly, tumor growth may occur.
• Mismatch-Repair Genes – These genes help recognize errors when DNA is copied to make a new cell. If the DNA does not "match" perfectly, these genes repair the mismatch and correct the error. If these genes are not working properly, however, errors in DNA can be transmitted to new cells, causing them to be damaged.

Usually the number of cells in body tissues is controlled with new cells formed for normal growth and development and dying cells replaced. Ultimately, cancer is a loss of this balance due to genetic alterations that "tip the balance" in favor of excessive cell growth.

Virus Exposure: Exposures to certain viruses, such as the human papillomavirus (HPV) and human immunodeficiency virus (HIV - the virus that causes AIDS), and the herpes virus have been linked to an increased risk of developing certain types of cancers. The virus alters a cell in some way and that cell then reproduces an altered cell and, eventually, these alterations become a cancer cell that reproduces more cancer cells. Cancer is not contagious and cannot be contracted from another person who has the disease.

Environmental Exposure: Environmental exposures such as pesticides, fertilizers, and power lines have been researched for a direct link to childhood cancers. There has been evidence of cancer occurring among non-related children in certain areas and/or cities. Whether prenatal or infant exposure to these agents causes cancer, or whether it is a coincidence, is unknown.

It usually cannot be explained 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. 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 risk of cancer is known the concern should be discussed with a specialist.

Over time, several factors may act together to cause normal cells to become cancerous. While considering the risks of getting cancer there are some things to keep in mind:

• 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.
• Cancer is not caused by an injury, such as a bump or bruise.
• 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.

Common Risk Factors

Some other common risk factors responsible for cancer are:

Tobacco: Tobacco use is the most preventable cause of death. 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, urinary 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.

Quitting is important for anyone who uses tobacco - even people who have used it for many years. The risk of cancer for people who quit is lower than the risk for people who continue to use tobacco. (But the risk of cancer is generally lowest among those who never used tobacco.) In addition, for people who have already had cancer, quitting may reduce the chance of getting another cancer.

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, Physical Inactivity or Obesity: 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.

Choose a diet rich in fruits and vegetables. Having a healthy diet, being physically active, and maintaining a healthy weight may help reduce cancer risk. A healthy diet includes plenty of foods that are high in fiber, vitamins, and minerals. This includes whole-grain breads and cereals and 5 to 9 servings of fruits and vegetables every day. Also, a healthy diet means limiting foods high in fat (such as butter, whole milk, fried foods, and red meat).

Be active and maintain a healthy weight: Physical activity can help control your weight and reduce body fat. Most scientists agree that it is a good idea for an adult to have moderate physical activity (such as brisk walking) for at least 30 minutes on 5 or more days each week.

Old Age: 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.

Sunlight: Ultraviolet (UV) radiation comes from the sun, sunlamps, and tanning booths. UV radiation can penetrate light clothing, windshields, and windows and can also get reflected by sand, water, snow, and ice. 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. Wear long sleeves, long pants, a hat with a wide brim, and sunglasses with lenses that absorb UV. Use sunscreen lotions with a sun protection factor (SPF) of at least 15. Sunscreens help but cannot substitute for sun avoidance or protective clothing.

Radiation Exposure: 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 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, a radioactive gas that you cannot see, smell, or taste, that forms in soil and rocks. People who work in mines may be exposed to radon. People exposed to radon are at increased risk of lung cancer.
• Medical procedures are a common source of radiation when doctors use radiation (low-dose x-rays) to take pictures of the inside of the body or when they 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 consult your doctor if you are concerned that you may be at risk for cancer due to radiation. 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 to their doctor about how radiation treatment could increase their risk of a second cancer later on.

Chemicals: People in certain professions (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.

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.

Unprotected Sex Or Shared 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 get vaccinated. 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 if you are infected. If so, the doctor may suggest treatment. Also, the doctor can tell you how to avoid infecting other people.

Viruses and Bacteria: Being infected with certain viruses or bacteria may increase the risk of developing cancer:

• Human papillomaviruses (HPVs) – HPV infection is the main cause of cervical cancer. It also may be a risk factor for other types of cancer.
• Hepatitis B and hepatitis C viruses – Liver cancer can develop after many years of infection with hepatitis B or hepatitis C.
• Human T-cell leukemia/lymphoma virus (HTLV-1) – Infection with HTLV-1 increases a person's risk of lymphoma and leukemia.
• Human immunodeficiency virus (HIV) – HIV is the virus that causes AIDS. People who have HIV infection are at greater risk of cancer, such as lymphoma and a rare cancer called Kaposi's sarcoma.
• Epstein-Barr virus (EBV) – Infection with EBV has been linked to an increased risk of lymphoma.
• Human herpesvirus 8 (HHV8) – This virus is a risk factor for Kaposi's sarcoma.
• Helicobacter pylori – This bacterium can cause stomach ulcers. It also can cause stomach cancer and lymphoma in the stomach lining. If you have stomach problems, see a doctor. Infection with H. pylori can be detected and treated.

Hereditary Genes: A majority of cancers develop because of changes (mutations) in genes. 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 a pattern of a certain type of cancer in the family is known it is advisable to consult a specialist who may suggest ways to try to reduce the risk of cancer. Certain genetic tests may also be suggested to check for certain inherited gene changes and detect the cancer early. Inheriting a gene change does not necessarily mean the development of cancer; it only indicates an increased chance of developing the disease.