Cancer and the Environment : Part 4

by National Cancer Institute

(Page 4 of 5)

Hormones

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 progesterone, may have increases in early-onset breast cancers and liver cancer, but have substantially reduced risks of endometrial and ovarian cancers.

Synthetic Hormones

The synthetic hormone tamoxifen is used in breast cancer therapies to prevent recurrence of disease or to prevent onset in women at high risk for this cancer, but it may increase the risk of endometrial cancer, strokes, and blood clots.

DES (diethylstilbestrol) is another synthetic hormone that was prescribed to pregnant women in the 1940s, 1950s, and 1960s. DES use was discontinued after scientists discovered that women taking it had an increased risk of breast cancer, and that girls born to women taking DES had an increased risk of rare types of vaginal and cervical cancer. Most physical or structural differences associated with exposure to DES are found in the reproductive tract, including a "hood" or collar on the cervix and a T-shaped uterus.

Solvents

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.

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

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.

Polycyclic Aromatic Hydrocarbons

These compounds (known as PAHs) come from the burning of carbon-based material. They are found in wood smoke, car exhaust, cigarette smoke, and charcoal-grilled foods. Sausages and roasted coffees may also contain PAHs. These compounds have been linked to increased risks of lung, skin, and urinary cancers.

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.

Other Carcinogens: Vinyl Chloride

Vinyl chloride is used in the plastics industry and has been associated with lung cancer and with angiosarcomas (blood-vessel tumors) of the liver and brain. Most people are not routinely exposed to vinyl chloride unless they work in plastics manufacturing plants. People who live close to such plants also may be exposed through contaminated air.

Other Carcinogens: Benzidine

Benzidine has been known to be associated with cancer since the 1920s. It is used in the production of dyes for paper, textiles, and leather. Exposure to these dyed products is not hazardous, however.

Other Carcinogens: Aflatoxins

Aflatoxins are produced by certain types of fungi that grow on grains and peanuts. People can also be exposed to aflatoxins by eating meat or dairy products from animals that ate contaminated feed. Exposure to high levels of aflatoxins increases the risk of liver cancer. Peanuts are screened for aflatoxins in most countries, including the United States.

Identifying Cancer-Causing Substances

Americans commonly use more than 100,000 chemicals, and this doesn't take into account mixtures or combinations of chemicals. Plus, some chemicals are altered by the atmosphere, water, or incineration.

Scientists have been working for several decades to identify substances that cause cancer. They have three ways to do this: through human studies, animal studies, and laboratory experiments.

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