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CarcinogensIn pathology, a carcinogen is any substance or agent that promotes cancer. Carcinogens are also often, but not necessarily, mutagensor teratogens. Carcinogens may cause cancer by altering cellular metabolism or damaging DNAdirectly in cells, which interferes with normal biologicalprocesses. Usually cells are able to detect this and attempt to repairthe DNA; if they cannot, they may undergo programmed cell deathto protect the organism. However, when the damage interferes with genes responsible for programmed cell death or perhaps encourages cell division, cancer may occur. Rapidly dividing cells, such as in skin, the stomachand intestinallining, breasttissue, and reproductive organs, are particularly sensitive to carcinogens due to any damaged DNA being quickly replicated. Unrepaired DNA replication can then lead to further accumulation of mutations between cell divisions. Most carcinogens consumed by humans are produced by plantsto prevent animalsfrom eating them (as are alkaloids). Plants containing large amounts of carcinogens include aristolochiaand bracken. AflatoxinB1, which is produced by the fungusAspergillusflavus growing on stored grains, nutsand peanut butter, is an example of a potent, naturally-occurring microbialcarcinogen. Cooking protein-rich food at high temperatures, such as broiling or barbecuing meats, can lead to the formation of many potent carcinogens that are comparable to those found in cigarrette smoke (i.e., benzo[a]pyrene). Pre-cooking meats in a microwave oven for 2-3 minutes before broiling can help minimize the formation of these carcinogens. DDT, benzene, kepone, EDB, asbestos, and the waste rock of oil-shalemining have all been classified as carcinogenic. As far back as the 1930s, industrialand tobaccosmoke were identified as sources of dozens of carcinogens, including benzopyrene, tobacco-specific nitrosaminessuch as nitrosonornicotine(NNN), and reactive aldehydessuch as formaldehyde— which is also a hazard in embalmingand making plastics. Vinyl chloridefrom PVC is a carcinogen. Certain viruses such as Hepatitis Band human papilloma viruseshave been found to cause cancer in humans. The first one shown to cause cancer in animals was chicken sarcoma virus, discovered in 1910by Peyton Roux. CERCLAidentifies all radionuclidesas carcinogens, although the nature of the emitted radiation(alpha, beta, or gamma, and the energy), its consequent capacity to cause ionizationin tissues, and the magnitude of radiation exposure, determine the potential hazard. For example, Thorotrast, an (incidentally-radioactive) suspensionpreviously used as a contrastmedium in x-raydiagnostics, is thought by some to be the most potent human carcinogen known because of its retention within various organsand persistent emission of alpha particles. Both Wilhelm Röntgenand Marie Curiedied of cancer caused by radiation exposure during their experiments. The non-reproducing cells of the (non-gametogenic) tissues of adult insectsare particularly resistant. Recent reports have implicated acrylamidein fried or overheated carbohydratefoods (such as french friesand potato chips) as a possible carcinogen. Studies are underway at the FDAand Europeanregulatory agencies to assess its potential risk. The charred residue on barbecuedmeats has been identified as a carcinogen, along with many other tars. Co-carcinogens are chemicals which do not separately cause cancer, but do so in specific combinations. IARCclassification of carcinogens
Further details can be found in the IARC Monographs. See also
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de:Karzinogen es:Carcinogénesis fr:Cancérogčne id:Karsinogen it:Agenti cancerogeni ms:Karsinogen nl:Carcinogeen zh:???? Categories: Biochemicals| Carcinogens| Oncology| Toxicology
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