Carcinogen Carcinogenic


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Carcinogen

pathology
Written By:

  • The Editors of Encyclopaedia Britannica
See Article History

Carcinogen, any of a number of agents that can cause cancer in humans. They can be divided into three major categories: chemical carcinogens (including those from biological sources), physical carcinogens, and oncogenic (cancer-causing) viruses .

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The routine monitoring of blood pressure levels is an important part of assessing an individual's health. Blood pressure provides information about the amount of blood in circulation and about heart function and thus is an important indicator of disease.

human disease: Carcinogenic agents

Chemicals capable of causing cancer arise from a variety of sources. These include certain synthetic chemicals used in industry, some natural compounds formed during the curing and burning of tobacco, compounds formed during the cooking of meat, and chemicals present in certain…

Most carcinogens, singly or in combination, produce cancer by interacting with DNA in cells and thereby interfering with normal cellular function. This ultimately results in the formation of a tumour (an abnormal tissue growth) that has the ability to spread ( metastasize ) from its site of origin and invade and cause dysfunction of other tissues, culminating in organ failure and death. The two primary mechanisms by which carcinogens initiate the formation of such tumours is via alterations in DNA that encourage cell division and that prevent cells from being able to self-destruct when stimulated by normal triggers, such as DNA damage or cellular injury (a process known as apoptosis ). There also exist carcinogens that induce cancer through nongenotoxic mechanisms, such as immunosuppression and induction of tissue-specific inflammation .

More than 400 chemical agents have been listed as carcinogenic, probably carcinogenic, or possibly carcinogenic by the International Agency for Research on Cancer (IARC), a branch of the World Health Organization that monitors cancer occurrence worldwide and performs epidemiological and laboratory investigations to understand the causes of cancer. Among the carcinogenic substances listed by IARC are a variety of chemical effluents from industry and environmental pollutants from automobiles, residences, and factories. One such example is acrylamide , which is considered a probable carcinogen in humans and is produced as a result of industrial processes and cooking certain foods at high temperatures. It can be released into the environment through its application in wastewater treatment and its use in grout and soil-stabilizer products. Other examples of chemical carcinogens include nitrosamines and polycyclic aromatic hydrocarbons, which are found in tobacco smoke and are associated with the development of lung cancer .

Physical carcinogens include ultraviolet rays from sunlight and ionizing radiation from X-rays and from radioactive materials in industry and in the general environment. Repeated local injury (e.g., wounding) or recurring irritation (e.g., chronic inflammation ) to a part of the body are other examples of potential physical carcinogens.

A number of viruses are suspected of causing cancer in animals, including humans, and are frequently referred to as oncogenic viruses. Examples include human papillomaviruses , the Epstein-Barr virus , and the hepatitis B virus, all of which have genomes made up of DNA. Human T-cell leukemia virus type I (HTLV-I), which is a retrovirus (a type of RNA virus), is linked to tumour formation in humans.

Some—not all—cancers are heritable in the sense that a predisposition exists, awaiting a convergence of carcinogenic influences for cancer to manifest itself. The identification and timely elimination of carcinogens can reduce the incidence of cancer.

Learn More in these related Britannica articles:

  • The routine monitoring of blood pressure levels is an important part of assessing an individual's health. Blood pressure provides information about the amount of blood in circulation and about heart function and thus is an important indicator of disease.

    human disease: Carcinogenic agents
    Chemicals capable of causing cancer arise from a variety of sources. These include certain synthetic chemicals used in industry, some natural compounds formed during the curing and burning of tobacco, compounds formed during the cooking of meat, and chemicals present in certain…
  • View through an endoscope of a polyp, a benign precancerous growth projecting from the inner lining of the colon.

    cancer: Cancer-causing agents
    Cancer-causing agents can be categorized into several groups, including oncogenic viruses, chemicals, and radiation. Particulate matter, which consists of minute solid particles and liquid droplets in the air (e.g., dust, secondhand smoke, and other forms of air pollution), and fibres, such as asbestos,…
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    …which induce enzymes that detoxify carcinogens and have been demonstrated to protect against cancer in animal studies. Dietary fibre in plant foods may also be protective: it dilutes potential carcinogens, binds to them, and speeds up transit time through the gut, thereby limiting exposure. Fruits and vegetables are rich in…
  • The bronchioles of the lungs are the site where oxygen is exchanged for carbon dioxide during the process of respiration. Inflammation, infection, or obstruction of the bronchioles is often associated with acute or chronic respiratory disease, including bronchiectasis, pneumonia, and lung abscesses.

    respiratory disease: Lung cancer
    The reason for the carcinogenicity of tobacco smoke is not known. Tobacco smoke contains more than 60 carcinogenic compounds, including harmful nitrosamines and polycyclic aromatic hydrocarbons. In addition to its single-agent effects, cigarette smoking greatly potentiates the cancer-causing proclivity of asbestos fibres, increases the risk of lung cancer due…
  • Lister, Joseph

    pharmaceutical industry: Toxicity tests
    Carcinogenicity (potential to cause cancer) studies are generally required if humans will use the drug for longer than six months. They usually are conducted concurrently with Phase 3 (large-scale safety and efficacy) clinical trials but may begin earlier if there is reason to suspect that…

More About Carcinogen

10 references found in Britannica articles

Assorted References

    • chemical carcinogens
      • In poison: Carcinogenesis
    • food substances
      • In nutritional disease: Cancer
    • formaldehyde
      • In formaldehyde
    • genetic mutations
      • In human genetic disease: Plants, fungi, and bacteria
    • major references
      • In human disease: Carcinogenic agents
      • In cancer: Cancer-causing agents
    • particulates
      • In air pollution: Fine particulates
    • pharmaceutical testing
      • In pharmaceutical industry: Toxicity tests
    • polycyclic aromatic hydrocarbons
      • In hydrocarbon: Nomenclature
    • respiratory diseases
      • In respiratory disease: Lung cancer

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