National Cancer Institute Understanding Cancer Series: Cancer and the Environment
Slide 2
|
|
|
|
What Is the Environment?
|
|
When most people think of the word "environment," they think of forests, oceans, or mountains. In cancer research, however, scientists define the environment as everything outside the body that enters and interacts with it. This interaction is called an exposure. So, environmental exposures can include such factors as sunshine, radiation, hormones, viruses, bacteria, and chemicals in the air, water, food, and workplace, as well as lifestyle choices like cigarette smoking, excessive alcohol consumption (more than 2 drinks/day), an unhealthful diet, lack of exercise, or sexual behavior that increases one's exposure.
Researchers have estimated that as many as 2 in 3 cases of cancer (67 percent) are linked to some type of environmental factor, including use--or abuse--of tobacco, alcohol, and food, as well as exposures to radiation, infectious agents, and substances in the air, water, and soil.
Slide 5
|
|
|
|
Different Exposures, Different Rates and Risks
|
|
Certain types of exposures are linked to specific cancers. For example, exposure to asbestos is linked to lung cancer, and exposure to benzidine (a chemical found in some dyes) is linked to bladder cancer. Exposure to carcinogens from tobacco use is linked to several types of cancer, including cancers of the lung, bladder, mouth, lip, throat, voice box, and esophagus.
Cigarette, cigar, and pipe smoking have been linked to more than a dozen types of cancer, including lung, mouth, bladder, colon, and kidney cancers. Chewing tobacco and snuff increase the risk of oral cancer, and second-hand smoke increases the risk of lung cancer.
Alcohol is another risk factor. Heavy drinkers have an increased risk of cancers of the mouth, throat, liver, voice box, and esophagus. There is also some evidence for an increased risk of breast cancer. Drinkers who also smoke may have an even higher risk of some oral and throat cancers. Drink in moderation, if at all: no more than one or two drinks per day.
Slide 17
|
|
|
|
Overweight and Exercise
|
|
Being overweight is an important lifestyle factor related to cancer risk. There are links between obesity and the risks of breast cancer (in older women), endometrial cancer, and cancers of the kidney, colon, and esophagus. Not being physically active increases the risk of colorectal and breast cancers.
Together, obesity and physical inactivity are linked to about 30 percent of the cases of colon, endometrial, kidney, and esophageal cancers, as well as 30 percent of breast cancers in older women.
Losing weight and exercising can help reduce your risk. Exercise at least 30 minutes a day, most days of the week. Exercise alone can decrease the risk of colon cancer and breast cancer. The goal should be for adults age 20 or older to keep their Body Mass Index (BMI) below 25. The BMI is a number that shows your body weight adjusted for your height.
The federal report on carcinogens doesn't discuss specific foods and cancer risk. However, studies show that consuming large quantities of red meat, preserved meats, salt-preserved meats, and salt probably increases the risk of stomach and colorectal cancers. Research also shows that a diet high in fruits and vegetables may decrease the risks of these cancers. And calorie restriction has been shown to reduce cancer risk for several cancer types.
Eat a healthy calorie-restricted diet rich in whole grains, fruits, and vegetables. Avoid consuming large amounts of fatty foods, red meats, salt, or salt-preserved food.
Some viruses are risk factors for cancer.
Human Papillomavirus
Certain strains of human papillomavirus (HPV), which are sexually transmitted, are the primary causes of cervical and anal cancer. Women who begin having sexual intercourse before age 17, or who have multiple sexual partners, are at greatest risk of HPV infection.
HPV may also be responsible for some cancers of the head and neck.
It's important to note that most people infected with HPV will not get cancer. Also, a vaccine is now available that can prevent infection with the strains of HPV that cause cervical cancer.
Hepatitis B and C
The hepatitis B and hepatitis C viruses are major causes of liver cancer worldwide. The viruses are transmitted through blood transfusions, injectable drug use, and unprotected sex. Vaccinations can protect against hepatitis B, but there is not yet a vaccine for hepatitis C.
Epstein-Barr virus causes mononucleosis. In people with weakened immune systems, it can also lead to some types of lymphoma.
People with weakened immune systems may also be at risk for a cancer called Kaposi's sarcoma if they are infected with human herpesvirus 8 (also known as Kaposi's sarcoma-associated herpesvirus, or KSHV). In the United States, KSHV infection is most common in homosexual men.
Radon, a naturally occurring radioactive gas found at low levels in most soil, is produced in the soil when the element uranium starts to break down. The health effects of high radon levels were first seen in the increased cases of lung cancer found in underground uranium miners in the United States and around the world. Radon gas seeps into cracks in the foundation of homes from surrounding soil; about 1 in 20 homes has elevated radon levels. Research estimates that about 20,000 lung cancer deaths every year may be linked to radon exposures in homes.
Check the radon levels in your home regularly. A ventilation system in your basement can dramatically reduce radon levels.
Atomic bombs and above-ground atomic bomb testing releases ionizing radiation that can increase cancer risk. People affected by the atomic bombs in Japan at the end of World War II, those living near nuclear testing sites in Nevada in the late 1950s and early 1960s, and those near the site of the Chernobyl nuclear power plant accident in the former Soviet Union in 1986 were all exposed to ionizing radiation.
Japanese atomic bomb survivors had increased rates of cancers of the breast, thyroid, lung, stomach, and other organs. People, especially children, exposed to iodine-131 (one form of radioactive iodine) both from the above-ground nuclear testing that has occurred in the United States and from the Chernobyl accident, have an increased risk of thyroid cancer.
Slide 26
|
|
|
|
Diagnostic and Screening X-rays
|
|
X-rays, mammograms, and radiation therapy all involve exposure to ionizing radiation. An X-ray of the chest exposes a patient to only a small amount of radiation--about the same as one gets from two airplane flights across the United States.
Studies have not shown an elevated cancer risk associated with X-rays taken to diagnose a disease or condition. One exception to this is in children whose mothers received X-rays while pregnant: the children were found to have increased risks of leukemia and other types of cancers. Because of this finding, X-rays to diagnose a condition in pregnant women are no longer recommended.
Talk with your doctor about the need for each X-ray that he or she suggests. Ask about shields to protect other parts of your body during an X-ray.
Some chemotherapy drugs used to treat cancer may increase the risk of second cancers later in life. Drugs that suppress the immune system--used to treat some cancers as well as to prepare patients receiving organ transplants--also are associated with increased risk of cancer, particularly lymphoma.
On the other hand, new estrogen-blocking drugs called aromatase inhibitors can decrease the recurrence of breast cancer.
Any medication carries risks and benefits, so always check with a health professional before starting a new drug.
Estrogen and progesterone are naturally occurring hormones. Given to women to treat the symptoms of menopause, they have been linked to increased risk of breast cancer.
Estrogen may also increase the risk of endometrial cancer, but progesterone helps protect against this increased risk. Estrogen and progestin (a synthetic form of progesterone) taken together are associated with increased risks of breast cancer, heart disease, stroke, and blood clots. Women who take oral contraceptives, which contain both estrogen and progestin, may have increases in early-onset breast cancers and liver cancer, but have substantially reduced risks of endometrial and ovarian cancers.
Solvents are used in paint removers, grease removers, paint thinners, and dry cleaning. The solvents benzene, carbon tetrachloride, chloroform, and methylene chloride have been linked to human cancer.
The strongest evidence linking a solvent to cancer involves benzene, which is also found in cigarette smoke and gasoline. It increases the risk of leukemia.
If you must work with solvents, work outside or make sure the area is well ventilated.
Slide 32
|
|
|
|
Fibers and Dusts
|
|
Some fibers and dusts can increase the risk of lung-related cancers.
Asbestos is linked to increased risks of lung cancer and mesothelioma, a rare cancer of the lining of the lung and abdominal cavity. In the past, asbestos was widely used in construction, but its use has been restricted. However, workers employed in construction, electrical work, or carpentry may still be exposed through renovations or asbestos-removal projects.
Other fibers and dusts (including silica dust and wood dust) can increase the risks of cancers of the lung, nasal cavities, and sinuses.
Wear a well-fitting mask if your job exposes you to fine particles, fibers, or dust.
Dioxins are byproducts of paper bleaching, smelting, and waste incineration. They are widespread in the environment because they break down very slowly. They also accumulate in fat cells. Most of our exposure to dioxins comes from eating dairy products, fish, and meat.
Slide 35
|
|
|
|
Other Carcinogens: Metals
|
|
Some metals--including arsenic, beryllium, cadmium, chromium, lead, and nickel--have been associated with several types of cancer, including lung, kidney, brain, skin, and liver cancers.
Human studies are the way to decide with the most certainty whether a substance causes cancer.
By following groups of people over time, researchers may be able to see whether certain exposures lead to cancer. They also compare a group of people who have been diagnosed with a type of cancer to another group of people without the disease. Sometimes the group with cancer has patterns of exposures very different from the patterns in the group without cancer.
Many environmental causes of cancer have first been noticed in the workplace, because people in certain occupations have higher exposures to some chemicals than do people in the general population.
Rodents (mice and rats) are commonly used in studies of environmental causes of cancer. They have a relatively short lifespan (2 to 3 years), and their bodies' responses to known cancer causing chemicals are similar to a human response. Dietary studies in rodents are more difficult, however, due to differences in the digestive systems of rodents and humans.
In animal studies, the chemical exposures are usually at much higher levels than would be seen with human exposure. If an extremely high level of exposure does not lead to cancer, researchers reason that the chemical most likely does not cause cancer at lower levels either.
How do scientists decide which exposures are high risk and which are low risk? Risk assessment involves three factors:
1. Potency: The potential of a given amount of a substance to cause cancer. Benzene, for example, is quite potent because even small amounts of it can increase cancer risk. Other compounds, such as chloroform, are less potent; they require higher exposures to increase the risk by the same degree.
2. Type of exposure: Whether the exposure is one-time (acute) or long-term (chronic), and whether it is unavoidable (in the workplace, for example, or in the air we breathe).
3. Dose response: A dose-response trend describes what happens to cancer risk as the level of exposure increases or decreases.
Slide 44
|
|
|
|
Occupational Cancer Risks
|
|
Certain occupations carry an increased cancer risk: these include painters; furniture makers; workers in the iron, steel, coal, and rubber industries; and workers involved in shoe manufacturing and repair.
Always use proper protective equipment when handling chemicals, and clean spills immediately.
Ask at your workplace about Material Safety Data Sheets, which contain information about hazardous substances.
The National Institute for Occupational Safety and Health (http://www.cdc.gov/niosh/) can answer many of your questions.
Slide 45
|
|
|
|
Cancer Screening for Early Detection
|
|
Cancer screening tests help detect cancer at an early stage, which allows treatment to occur before the cancer spreads.
Get screened regularly for these cancers:
- Colon/rectum: Tests include the fecal occult blood test, sigmoidoscopy, and colonoscopy.
- Breast: The standard screening test is a mammogram, or X-ray of the breast tissue.
- Cervix: The standard screening test is the Pap smear.
Guidelines for when testing should begin and how often it should occur may be different for each person, so talk with your doctor about what's right for you.
Also talk with your health care provider about exposures at work and at home, and discuss whether your family or personal history may put you at risk for certain types of cancer. Your doctor may recommend other cancer screening tests as well.
|