This fact sheet will answer some common questions about cancer. Many people wonder if the environment they live in “causes cancer.” To answer such difficult questions, it is first necessary to understand what cancer is, how it develops and what factors contribute to cancer.
What is cancer?
Cancer is not a single disease. It is a group of more than 200 different diseases. Cancer is an uncontrolled growth of cells that disrupts body tissues and organs. Cancerous cells are not normal in their structure and function. They grow and multiply to form tumors that invade local tissues and sometimes scatter throughout the body. In the beginning, there are no warning signs to alert us to the disease. Later, the signs of cancer are related to the location of the tumor. As cancer progresses, it commonly causes loss of muscle tissue, pale skin, pain, fatigue and loss of appetite.
How widespread is cancer?
It is estimated that one out of every two men and one of every three women will have cancer in their lifetimes. About one in four persons will die of cancer. The American Cancer Society estimates that about 570,000 cancer deaths occur each year in the United States. Cancer is the second leading cause of death after heart disease.
Which cancers cause the most deaths?
In the United States, lung cancer is the leading cause of cancer-related deaths for both sexes, followed by prostate cancer in males and breast cancer in females. For children younger than 15 years old, cancer is the fifth leading cause of death after accidents. Leukemia and cancers of the brain and central nervous system are the leading cancers in children in this age group.
How many kinds of cancer are there?
There are many types of cancer because cancerous cells can grow anywhere in the body. The location of the cancer and the type of tissue involved helps to give the disease a specific name, such as lung cancer, ovarian cancer, breast cancer and prostate cancer. Other examples are melanoma (involving cells that contain skin pigment called melanin) and leukemia (involving the white blood cells).
How does cancer develop?
Cancer is a process with three steps: initiation, promotion and progression. Each step plays a vital role in stopping the cancer process. Since a period of many years usually exists between the initiation of the cancer process and the onset of the symptoms, cancer prevention methods like risk control and early detection are most effective in the first two steps.
The first step involves changes to the genetic code (DNA) of a cell called initiation. Initiation is simply a mistake (mutation). The mistake may appear on a chromosome, or it could turn up in a gene segment of DNA. Usually, initiation by itself is not enough to produce cancer; the body’s repair systems can replace damaged sections of DNA, which allow the cell to recover under normal circumstances. If the cell reproduces while the DNA is damaged, more abnormal cells can be made that may develop into cancer.
The altered cells undergo more changes that may require an additional substance called a promoter. A promoter is something that speeds up the pace of cell division, which can create more genetic mutations. A promoter may be a hormone such as estrogen or a toxic substance such as a chemical in tobacco smoke.
The last step is progression , which means that the cells have begun to grow out of control and is the basis for all cancers. The out of control cells form a tumor. A tumor is simply a mass of abnormal cells that keep growing and can extend into nearby tissues or spread to other parts of the body. How quickly a cancer progresses is determined by body conditions, such as hormones, and by genetic factors.
No one completely understands this process, but certain aspects of a person’s lifestyle can be linked to cancer formation.
What causes cancer?
There is no single cause of cancer. Cancer development depends on things such as family history (genetics), health, nutrition, personal habits and the environment. Genetic factors by themselves probably account for only a small fraction of cancers. Genetic factors do have an important influence on a person’s chance of developing cancer when combined with outside factors. These factors are either voluntary (such as cigarette smoking, diet, and sexual behavior) or involuntary (such as breathing polluted air or drinking contaminated water).
What factors contribute to cancer?
Cigarette smoking is the leading cause of cancer. Cigarette smoke contains more than 3,800 individual chemicals, and more than 40 are carcinogenic (cancer causing).
Portions of the diet, especially fatty foods and alcoholic beverages , also are linked to cancer.
Skin exposure to ultraviolet radiation in sunlight is the primary cause of melanoma, a skin cancer.
Sexual behavior that helps spread sexually transmitted diseases is closely linked to cervical cancer in women.
Environmental pollution by chemicals in drinking water, air, food and in the workplace may contribute to cancer. The harmful health effects of chemicals depend on the dose, strength of the chemical compound, the length of exposure and the general health of the individual. Outside the workplace, very few cases of cancer are believed to be caused by exposure to chemicals in the environment.
Most cancers may be prevented through the identification and control of external factors. Approximately 30 percent of cancers are linked to cigarette smoking. The remaining 70 percent are likely the result of interaction among various factors.
How do chemicals cause cancer?
Some chemicals in the environment are toxic substances that can produce cancer in humans and animals. Most chemicals act by causing the initiation step in the cancer process (altering the DNA), but they also can act as promoters.
What cancers are caused by chemicals?
Most cancer-causing chemicals were first recognized in workplace settings. The workplace is unique because workers are often exposed to large amounts of chemicals over long periods of time. The first association of cancer with the workplace occurred in 1775. A London doctor related cases of cancer of the scrotum among young chimney sweeps to their exposure to soot. Other cause-and-effect relationships have been noted in workers between –
- benzene and leukemia;
- asbestos and lung cancer; and
- vinyl chloride and liver cancer.
Workers may be exposed to a combination of cancer-causing chemicals (carcinogens), which increases their cancer risk. The risk of lung cancer in asbestos workers who also smoke cigarettes is at least 50 times higher than the risk in nonsmoking asbestos workers. Reducing chemical exposure can prevent most work-related cancers.
How are chemicals tested for cancer causing properties?
Studies and experiments with laboratory animals are the main sources that identify whether exposure to a certain chemical causes cancer. Laboratory tests often use doses much higher than those found in the environment. Scientists then apply the animal results to humans to calculate the “cancer risk” for the tested chemical. This process is difficult because there is no complete match between cancer in animals and cancer in humans.
If I am exposed to a carcinogen, will I get cancer?
Cancer development is a complex process that occurs over a long period of time, and is influenced by many factors. There are many different substances that act as carcinogens. Some, like asbestos, are linked to many different human cancers and risk of cancer development is high. Therefore, the risk of getting cancer from exposure depends upon the type of carcinogen and length of exposure.
The good news is that if exposure to carcinogens is stopped soon enough, the body can stop or reverse the cancer process.
What can you do to reduce your risk of getting cancer?
Scientific evidence shows that lifestyle choices, a healthy diet, good nutrition and physical activity can reduce cancer risk. It is never too late to make these changes, but changing long-term behavior can be difficult. You must be persistent over time to reduce your risk of getting cancer. The American Cancer Society recommends the following –
- Avoid using tobacco products, such as cigarettes, snuff and chewing tobacco. This is especially important for individuals who drink alcoholic beverages. Cancer risk of tobacco and alcohol combined is greater than the sum of their individual effects.
- Choose most of the foods you eat from plant sources. Eat five or more servings of fruits and vegetables each day. Eat other foods, such as breads, cereals, grain products, rice, pasta or beans, several times each day. Wash fresh fruits and vegetables before eating.
- Limit your intake of high-fat foods, particularly from animal sources. Choose foods low in fat and limit consumption of high-fat red meats. Choose baked and broiled meats, seafood and poultry, rather than fried food.
- Be physically active and achieve and maintain a healthy weight. Be moderately active for at least 30 minutes on most days of the week. Stay within your healthy weight range. Be aware that many fat-free cakes, cookies, snack foods and other desserts are high in calories.
- Limit consumption of alcoholic beverages. Men should have no more than two drinks per day. Women should have no more than one drink per day because they absorb alcohol more readily and are usually smaller in body size.
- Avoid or reduce exposure to sunlight, particularly in childhood. Reduce your sun exposure by avoiding sun during the middle of the day, wearing protective hats and clothing, seeking shade while outdoors and applying sunscreen to uncovered skin.
- Follow safety rules and regulations at your workplace. If possible, carcinogens should be replaced with safer substitutes. Workers should handle hazardous materials in a ventilated area and be trained to protect themselves. Personal protective clothing and respirators may be required.
Where can I get more information?
If you have concerns about your health and cancer, talk to your doctor about ways to reduce your cancer risk.