Other Cancer

Causes of Cancer

The more we can learn about the causes of cancer, the more likely we are to find ways to prevent it. In the laboratory, scientists explore possible causes of cancer and try to determine exactly what happens in cells when they become cancerous. Researchers also study patterns of cancer in the population to look for risk factors for cancer, conditions that increase the chance that cancer might occur. They also look for protective factors, things that decrease the risk of cancer.

Even though doctors can seldom explain why one person gets cancer and another does not, 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 over time. It is a result of a complex mix of factors related to lifestyle, heredity, and environment. A number of risk factors that increase a person's cancer risk have been identified. Many types of cancer are related to the use of tobacco, what people eat and drink, exposure to ultraviolet (UV) radiation from the sun, and, to a lesser extent, exposure to cancer-causing agents (carcinogens) in the environment and the workplace. Some people are more sensitive than others to factors that can be potential causes of cancer.

Still, most people who get the disease have none of the known risk factors of cancer. And most people who do have risk factors do not get the disease. Some risk factors of cancer can be avoided. Others, such as inherited risk factors, are unavoidable, but it may be helpful to be aware of them. People can help protect themselves by avoiding known risk factors whenever possible. They can also talk with their doctor about regular checkups and about whether cancer screening tests could be of benefit.

These are some of the factors that increase the likelihood of cancer:

  • Tobacco - Smoking tobacco, using smokeless tobacco, and being regularly exposed to environmental tobacco smoke 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.

  • Diet - Researchers are exploring how dietary factors play a role in the development of cancer. Some evidence suggests a link between a high-fat diet and certain types of cancer, such as cancers of the colon, uterus, and prostate. Being seriously overweight may be linked to breast cancer among older women and to cancers of the prostate, pancreas, uterus, colon, and ovary. On the other hand, some studies suggest that foods containing fiber and certain nutrients may help protect against some types of cancer.

  • Ultraviolet (UV) radiation - UV radiation from the sun causes premature aging of the skin and skin damage that can lead to skin cancer. (Two types of ultraviolet radiation -- UVA and UVB -- are explained in the Dictionary.) Artificial sources of UV radiation, such as sunlamps and tanning booths, also can cause skin damage and probably an increased risk of skin cancer.

  • Alcohol - Heavy drinkers have an increased risk of cancers of the mouth, throat, esophagus, larynx, and liver. (People who smoke cigarettes and drink heavily have an especially high risk of getting these cancers.) Some studies suggest that even moderate drinking may slightly increase the risk of breast cancer.

  • Ionizing radiation - Cells may be damaged by ionizing radiation from x-ray procedures, radioactive substances, rays that enter the Earth's atmosphere from outer space, and other sources. In very high doses, ionizing radiation may cause cancer and other diseases. Studies of survivors of the atomic bomb in Japan show that ionizing radiation increases the risk of developing leukemia and cancers of the breast, thyroid, lung, stomach, and other organs.

  • Chemicals and other substances - Being exposed to substances such as certain chemicals, metals, or pesticides can increase the risk of cancer. Asbestos, nickel, cadmium, uranium, radon, vinyl chloride, benzidene, and benzene are examples of well-known carcinogens. These may act alone or along with another carcinogen, such as cigarette smoke, to increase the risk of cancer. 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 or minimize contact with dangerous materials.

  • Hormone replacement therapy (HRT) - Doctors may recommend HRT, using either estrogen alone or estrogen in combination with progesterone, to control symptoms (such as hot flashes and vaginal dryness) that may occur during menopause. Studies have shown that the use of estrogen alone increases the risk of cancer of the uterus. Therefore, most doctors prescribe HRT that includes progesterone along with low doses of estrogen. Progesterone counteracts estrogen's harmful effect on the uterus by preventing overgrowth of the lining of the uterus; this overgrowth is associated with taking estrogen alone. (Estrogen alone may be prescribed for women who have had a hysterectomy, surgery to remove the uterus, and are, therefore, not at risk for cancer of the uterus.) Other studies show an increased risk of breast cancer among women who have used estrogen for a long time; and some research suggests that the risk might be higher among those who have used estrogen and progesterone together.

  • Diethylstilbestrol (DES) - DES is a synthetic form of estrogen that was used between the early 1940s and 1971. Some women took DES during pregnancy to prevent certain complications. Their DES-exposed daughters have an increased chance of developing abnormal cells (dysplasia) in the cervix and vagina. In addition, a rare type of vaginal and cervical cancer can occur in DES-exposed daughters. DES daughters should tell their doctor about their exposure. They should also have pelvic exams by a doctor familiar with conditions related to DES.

  • Close relatives with certain types of cancer - Some types of cancer (including melanoma and cancers of the breast, ovary, prostate, and colon) tend to occur more often in some families than in the rest of the population. It is often unclear whether a pattern of cancer in a family is primarily due to heredity, factors in the family's environment or lifestyle, or just a matter of chance.

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