Carcinogen

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Carcinogen Summary

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Carcinogen

A carcinogen is any substance or agent that produces or induces the development of cancer. Carcinogens are known to affect and initiate metabolic processes at the level of cellular DNA.

Cancer accounts for slightly over 20% of all deaths each year. It is estimated that one out of every four Americans will develop cancer eventually and that six out of 10 in this group will die from the disease itself or complications arising from the disease. Half of all cancer deaths occur before the age of 65. Among women between 30 and 40 and children between three and 14, cancer is the leading cause of death next to accidents. It is the most frequent cause of death among Americans under 35 years of age.

The testing of chemicals as cancer-producing agents began with the observation of Sir Percival Pott in 1775 that scrotal cancer in young chimney sweeps resulted from the lodgement of soot in the folds of their scrotums. Pott was the first to link an environmental agent, coal tar, to cancer growth. In 1918 scientists began to test chemical derivatives for their cancer-causing efficacy. These first experiments looked at polycyclic hydrocarbons, specifically benzo(a)pyrene found in coal tar, and they demonstrated that a certain degree of exposure to coal tar produced cancer in laboratory rats. In 1908, Vilhelm Ellerman and Oluf Bang of Denmark reported that an infectious agent could cause cancer, after they found that a leukemia-like blood disease was transmitted among domestic fowl via a virus. In 1911, Peyton Rous established a viral cause for a cancer called sarcoma in domestic fowl, and he was awarded a Nobel Prize for this discovery some 55 years later. In 1932, Lacassagne reported that estrogen injections caused mammary cancer in mice. This opened up investigation into the role hormones played in the development of various types of cancers.

In 1896, Wilhelm Roentgen discovered the x ray, a radioactive emission capable of penetrating many solid materials including the human body. x rays quickly found use as a diagnostic tool in medicine; but operators of x ray devices, unaware of their harmful effects, determined the proper intensity of the beams by repeatedly exposing their hands to the rays. Many operators of x ray equipment began to suffer from cancer of the hand, and Roentgen himself died of cancer. The most dramatic environmental link to cancer induced by radioactivity was observed after the bombing of Hiroshima, Japan when there was a radical increase in leukemia type cancers among people exposed to the atomic blast.

Environmental agents such as toxic chemicals and radiation are considered responsible for about 85% of all cancer cases. A great many environmental agents such as synthetic chemicals, sunlight (exposure to UV and UVB rays), air pollutants, heavy metals, x rays, high-fat diet, chemical pesticides, and cigarette smoking are known to be carcinogenic. Surveys carried out on the geographic incidence of cancer indicate that certain types of cancer are far more common in heavily industrialized areas. New Jersey, the site of approximately 1,200 chemical plants and related industries, has the highest overall cancer rate in the United States.

Tobacco use, particularly cigarette smoking, is now recognized as the leading contributor to cancer mortality in the United States. Currently one third of all cancer deaths are due to lung cancer, and of the 130,000 new lung cancer victims diagnosed each year, 80% are cigarette smokers. Several years ago, the primary cause of cancer among women was breast cancer—but by the late 1980s, lung cancer had surpassed breast cancer as the leading cause of death among women. Current controversy rages over the role of secondary smoke as a contributing cause of cancer among nonsmokers exposed to cigarette smoke.

Dietary factors have been extensively investigated, and experiments have implicated everything from coffee to charcoal broiled meat to peanut butter as possible carcinogens. A major concern among meat producers was the use of diethylstilbestrol (DES) as a source for beefing up cattle. DES is a synthetic hormone that increases the rate of growth in cattle. In the 1960s, DES was fed to about three fourths of all the cattle raised in the United States. It was also used to prevent miscarriages in women until 1966, when it was shown to be carcinogenic in mice. DES is now linked to vaginal and cervical cancers in women born between 1950 and 1966 whose mothers took DES during their pregnancies.

In 1971, DES was banned for use in cattle by the Food and Drug Administration (FDA), but the federal courts reversed the ban, contending that DES posed no danger since it was not directly added to foods but was administered only to cattle. When the FDA subsequently showed that measurable quantities remained present in slaughtered cattle, the courts reinstated the ban. But the issue of using growth additives in meat production remains unresolved today. Environmentalists are still concerned that known carcinogenic chemicals used to "beef up" cattle are being consumed by humans in various meat products, though no direct links have yet been established. In addition, various food additives, such as coal tar dyes used for artificial coloring and food preservatives, have produced cancer in laboratory animals. As yet there is no evidence indicating that human cancer rates are rising because of these substances in food.

Air pollution has been extensively investigated as a possible carcinogen and it is known that people living in cities larger than 50,000 run a 33% higher risk of developing lung cancer than people who live in other areas. The reasons behind this phenomenon, referred to as the "urban factor," have never been conclusively determined. Areas with populations exceeding 50,000 tend to have more industry, and air pollutants can have a profound effect in regions such as New Jersey where they are highly concentrated.

Occupational exposure to carcinogenic substances accounts for an estimated 2–8% of diagnosed cancers in the United States. Until passage of the Toxic Substances Control Act in 1976, which gave the federal government the power to require testing of potentially hazardous substances before they go on the market, hundreds of new chemicals with unknown side effects came into industrial use each year. Substances such as asbestos are estimated to cause 30–40% of all deaths among workers who have been exposed to it. Vinyl chloride, a basic ingredient in the production of plastics, was found in 1974 to induce a rare form of liver cancer among exposed workers. Anaesthetic gases used in operating rooms have been traced as the reason nurse anesthetists develop leukemia and lymphoma at three times the normal rate with an associated higher rate of miscarriage and birth defects among their children. Benzene, an industrial chemical long known as a bone-marrow poison, has been shown to induce leukemia as well. A major step forward in the regulation of these potential cancer causing agents is the implementation by the Occupational Safety and Health Administrations (OSHA) of the Hazard Communication Standard in 1983, intended to provide employees in manufacturing industries access to information concerning hazardous chemicals encountered in the workplace.

With the erosion of the ozone layer of our atmosphere, increased concern about over-exposure to ultraviolet radiation and its subsequent effect on the formation of skin cancer has developed. The EPA estimates that a five% ozone depletion in the stratosphere would result in a substantial increase in a variety of skin cancers. This would include an average of two million extra cases of basal-cell and squamous-cell skin cancers a year and an additional 30,000 cases of the often fatal melanoma skin cancer, which currently kills 9,000 Americans per year.