Difference between revisions of "Carcinogen" - New World Encyclopedia

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In [[pathology]], a '''carcinogen''' is any substance or agent that promotes [[cancer]]. Carcinogens are also often, but not necessarily, [[mutagen]]s or [[teratogen]]s.
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The term '''carcinogen''' refers to any substance, [[radionuclide]] or radiation which is an agent directly involved in the promotion of [[cancer]] or in the facilitation of its propagation. This may be due to [[genome|genomic instability]] or to the disruption of cellular [[metabolic]] processes. Several radioactive substances are considered carcinogens, but their carcinogenic activity is attributed to the radiation, for example [[gamma ray]]s or [[alpha particle]]s, which they emit. Common examples of carcinogens are inhaled [[asbestos]] and [[tobacco]] smoke.
  
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Carcinogens may cause cancer by altering cellular metabolism or damaging [[DNA]] directly in [[cell (biology)|cell]]s, which interferes with normal [[biology|biological]] processes. Usually cells [[bracken]]. [[Aflatoxin]] B<sub>1</sub>, which is produced by the [[fungus]] ''[[Aspergillus]] flavus'' growing on stored [[cereal|grain]]s, [[nut (fruit)|nut]]s and [[peanut butter]], is an example of a potent, naturally-occurring [[microbe|microbial]] carcinogen. 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.
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==Carcinogenity==
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[[Cancer]] is a disease where damaged cells of the patient's body do not undergo [[programmed cell death]], but their growth is no longer controlled and their metabolism is altered. Carcinogens may increase the risk of getting cancer by altering cellular metabolism or damaging [[DNA]] directly in [[cell (biology)|cell]]s, which interferes with [[biology|biological]] processes, and induces the uncontrolled, malignant division ultimately leading to the formation of tumors. Usually DNA damage, if too severe to repair, leads to [[programmed cell death]], but if the programmed cell death pathway is damaged, then the cell cannot prevent itself from becoming a cancer cell.
  
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[[Benzene]], [[kepone]], [[EDB]], [[asbestos]], and the waste rock of [[oil shale|oil-shale]] mining have all been classified as carcinogenic. As far back as the 1930s, [[Industry|industrial]] and [[tobacco]] smoke were identified as sources of dozens of carcinogens, including [[benzopyrene]], tobacco-specific [[nitrosamine]]s such as [[nitrosonornicotine]] (NNN), and reactive [[aldehyde]]s such as [[formaldehyde]] &mdash; which is also a hazard in [[embalming]] and making [[plastic]]s. [[Vinyl chloride]] from PVC is a carcinogen. Certain viruses such as [[Hepatitis B]] and [[human papilloma virus]]es have been found to cause cancer in humans. The first one shown to cause cancer in animals was [[chicken sarcoma virus]], discovered in 1910 by [[Peyton Roux]].
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There are many natural carcinogens. [[Aflatoxin]] B<sub>1</sub>, which is produced by the [[fungus]] ''[[Aspergillus]] flavus'' growing on stored [[cereal|grain]]s, [[nut (fruit)|nut]]s and [[peanut butter]], is an example of a potent, naturally-occurring [[microbe|microbial]] carcinogen. Certain viruses such as [[Hepatitis B]] and [[human papilloma virus]]es have been found to cause cancer in humans. The first one shown to cause cancer in animals was [[Rous sarcoma virus]], discovered in [[1910]] by [[Peyton Rous]].  
  
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[[CERCLA]] identifies all [[radionuclide]]s as carcinogens, although the nature of the emitted [[Radioactive decay|radiation]] ([[alpha particle|alpha]], [[beta particle|beta]], or [[gamma ray|gamma]], and the energy), its consequent capacity to cause [[ionization]] in tissues, and the magnitude of radiation exposure, determine the potential hazard. For example, [[Thorotrast]], an (incidentally-radioactive) [[suspension (chemistry)|suspension]] previously used as a [[contrast]] medium in [[x-ray]] diagnostics, is thought by some to be the most potent human carcinogen known because of its retention within various [[organ (biology)|organ]]s and persistent emission of alpha particles. Both [[Wilhelm Conrad Röntgen|Wilhelm Röntgen]] and [[Marie Curie]] died of cancer caused by radiation exposure during their experiments. The non-reproducing cells of the (non-[[gamete|gametogenic]]) tissues of adult [[insect]]s are particularly resistant.
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[[Benzene]], [[kepone]], [[1,2-Dibromoethane|EDB]], [[asbestos]], and the waste rock of [[oil shale]] mining have all been classified as carcinogenic.{{Fact|date=April 2007}} As far back as the [[1930s]], [[Industry|industrial]] and [[tobacco]] smoke were identified as sources of dozens of carcinogens, including [[benzopyrene]], tobacco-specific [[nitrosamine]]s such as [[nitrosonornicotine]], and reactive [[aldehyde]]s such as [[formaldehyde]] &mdash; which is also a hazard in [[embalming]] and making [[plastic]]s. [[Vinyl chloride]], from which [[PVC]] is manufactured, is a carcinogen and thus a hazard in PVC production.
  
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Recent reports have implicated [[acrylamide]] in fried or overheated [[carbohydrate]] foods (such as [[french fries]] and [[potato chips]]) as a possible carcinogen. Studies are underway at the [[US Food and Drug Administration|FDA]] and [[Europe]]an regulatory agencies to assess its potential risk. The charred residue on [[barbecue]]d meats has been identified as a carcinogen, along with many other [[tar]]s.
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[[Co-carcinogen]]s are chemicals which do not separately cause cancer, but do so in specific combinations.
  
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Co-carcinogens are chemicals which do not separately cause cancer, but do so in specific combinations.
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DNA is nucleophilic, therefore soluble carbon electrophiles are carcinogenic, because DNA attacks them. For example, some [[alkene]]s are [[Toxication|toxicated]] by human enzymes to produce an [[Electrophile|electrophilic]] epoxide. DNA attacks the epoxide, and is bound permanently to it.  This is the mechanism behind the carcinogenity of [[benzopyrene]] in tobacco smoke, other aromatics, aflatoxin and mustard gas.
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After the carcinogen enters the body, the body makes an attempt to eliminate it through a process called [[biotransformation]]. The purpose of these reactions is to make the carcinogen more [[water-soluble]] so that it can be removed from the body. But these reactions can also convert a less toxic carcinogen into a more toxic one.
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==Radiation==
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[[CERCLA]] identifies all [[radionuclide]]s as carcinogens, although the nature of the emitted [[Radioactive decay|radiation]] ([[alpha particle|alpha]], [[beta particle|beta]], or [[gamma ray|gamma]], and the energy), its consequent capacity to cause [[ionization]] in tissues, and the magnitude of radiation exposure, determine the potential hazard. For example, [[Thorotrast]], a (incidentally-radioactive) [[suspension (chemistry)|suspension]] previously used as a [[Radiocontrast|contrast]] medium in [[x-ray]] diagnostics, is thought by some to be the most potent human carcinogen known because of its retention within various [[organ (biology)|organ]]s and persistent emission of alpha particles. Both [[Wilhelm Conrad Röntgen|Wilhelm Röntgen]] and [[Marie Curie]] died of cancer caused by radiation exposure during their experiments.
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Not all types of electromagnetic radiation are carcinogenic.  Low-energy waves on the [[electromagnetic spectrum]] are generally not, including [[radio waves]], [[microwave radiation]], [[infrared radiation]], and [[visible light]].  Higher-energy radiation, including [[ultraviolet radiation]] (present in [[sunlight]]), [[x-rays]], and [[gamma radiation]], generally ''is'' carcinogenic, if received in sufficient doses.
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==Carcinogens in prepared food==
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Cooking food at high temperatures, for example [[broiling]] or [[barbecuing]] meats, can lead to the formation of minute quantities of many potent carcinogens that are comparable to those found in cigarette smoke (i.e., [[benzopyrene]]).<ref>Wei Zheng, Deborah R Gustafson, Rashmi Sinha, James R Cerhan, ''et al.'' "Well-done meat intake and the risk of breast cancer." ''Journal of the National Cancer Institute''. Oxford: Nov 18, 1998.Vol. 90, Iss. 22;  pg. 1724, 6 pgs.</ref> Charring of food resembles [[coking]] and tobacco [[pyrolysis]] and produces similar carcinogens. There are several carcinogenic pyrolysis products, such as polynuclear aromatic hydrocarbons, which are converted by human [[enzyme]]s into [[epoxide]]s, which attach permanently to DNA. Pre-cooking meats in a [[microwave oven]] for 2-3 minutes before broiling shortens the time on the hot pan, which can help minimize the formation of these carcinogens.
 +
 
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Recent reports have found that the known animal carcinogen [[acrylamide]] is generated in fried or overheated [[carbohydrate]] foods (such as [[french fries]] and [[potato chips]]). Studies are underway at the [[US Food and Drug Administration|FDA]] and [[Europe]]an regulatory agencies to assess its potential risk to humans. The charred residue on [[barbecue]]d meats has been identified as a carcinogen, along with many other [[tar]]s.
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Nevertheless, the fact that the food contains minute quantities doesn't necessarily mean that there is a significant hazard. The gastrointestinal tract sheds its outer layer continuously to protect itself from [[carcinoma]]s, and has a high activity of detoxifying enzymes. The lungs are not protected in this manner, therefore smoking is much more hazardous.{{Facts|date=June 2007}}
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==Classification of carcinogens==
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Carcinogens can be classified as genotoxic or nongenotoxic. [[Genotoxin]]s cause irreversible genetic damage or mutations by binding to [[DNA]]. Genotoxins include chemical agents like [[N-Nitroso-N-Methylurea]] (MNU) or non-chemical agents such as [[ultraviolet light]] and [[ionizing radiation]]. Certain viruses can also act as carcinogens by interacting with DNA.
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[[Nongenotoxin]]s do not directly affect DNA but act in other ways to promote growth. These include hormones and some organic compounds.<ref>{{cite news | first= | last= | coauthors= | title=The Gale Encyclopedia of Cancer: A guide to Cancer and its Treatments, Second Edition.  Page no. 137 }}</ref>
  
 
== [[International Agency for Research on Cancer|IARC]] classification of carcinogens ==
 
== [[International Agency for Research on Cancer|IARC]] classification of carcinogens ==
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*[[List of IARC Group 1 carcinogens|Group 1]]: the agent (mixture) is carcinogenic to humans. The exposure circumstance entails exposures that are carcinogenic to humans.
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*[[List of IARC Group 1 carcinogens|Group 1]]: the agent (mixture) is definitely carcinogenic to humans. The exposure circumstance entails exposures that are carcinogenic to humans.
 
*[[List of IARC Group 2A carcinogens|Group 2A]]: the agent (mixture) is probably carcinogenic to humans. The exposure circumstance entails exposures that are probably carcinogenic to humans.
 
*[[List of IARC Group 2A carcinogens|Group 2A]]: the agent (mixture) is probably carcinogenic to humans. The exposure circumstance entails exposures that are probably carcinogenic to humans.
 
*[[List of IARC Group 2B carcinogens|Group 2B]]: the agent (mixture) is possibly carcinogenic to humans. The exposure circumstance entails exposures that are possibly carcinogenic to humans.
 
*[[List of IARC Group 2B carcinogens|Group 2B]]: the agent (mixture) is possibly carcinogenic to humans. The exposure circumstance entails exposures that are possibly carcinogenic to humans.
 
*[[List of IARC Group 3 carcinogens|Group 3]]: the agent (mixture or exposure circumstance) is not classifiable as to its carcinogenicity to humans.
 
*[[List of IARC Group 3 carcinogens|Group 3]]: the agent (mixture or exposure circumstance) is not classifiable as to its carcinogenicity to humans.
 
*[[List of IARC Group 4 carcinogens|Group 4]]: the agent (mixture) is probably not carcinogenic to humans.
 
*[[List of IARC Group 4 carcinogens|Group 4]]: the agent (mixture) is probably not carcinogenic to humans.
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Further details can be found in the [http://www-cie.iarc.fr/ IARC Monographs].
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Further details can be found in the [http://monographs.iarc.fr/ IARC Monographs].
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==[[Environmental Protection Agency|EPA]] classification of carcinogens==
 
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*Group A: Human Carcinogen
 
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*Group B: Probable Human Carcinogen
 
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*Group C: Possible Human Carcinogen
 
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*Group D: Not classifiable as to Human Carcinogenicity
 
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*Group E: Evidence of Non-Carcinogenicity for Humans
 
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Further details can be found in the EPA [http://www.pested.psu.edu/infocenter/issues/fqpacanctab.pdf List of Chemicals Evaluated for Carcinogenic Potential].
 
  
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==Notes==
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<div class="references-small">
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<references />
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</div>
 
== See also ==
 
== See also ==
 
* [[International Agency for Research on Cancer]]
 
* [[International Agency for Research on Cancer]]
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* [[Mutagen]]
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* [[Teratogen]]
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* [[Warburg's hypothesis]]
  
 
== External links ==
 
== External links ==
 
* [http://ntp.niehs.nih.gov/index.cfm?objectid=03C9B512-ACF8-C1F3-ADBA53CAE848F635 U.S. National Toxicology Program's Report on Carcinogens]
 
* [http://ntp.niehs.nih.gov/index.cfm?objectid=03C9B512-ACF8-C1F3-ADBA53CAE848F635 U.S. National Toxicology Program's Report on Carcinogens]
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* [http://www.scorecard.org/health-effects/chemicals.tcl?short_hazard_name=cancer&all_p=t Recoginzed Carinogens]
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* [http://www.scorecard.org/health-effects/chemicals.tcl?short_hazard_name=cancer&all_p=t Recognized Carcinogens]
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*[http://www.cancer.org/docroot/PED/content/PED_1_3x_Known_and_Probable_Carcinogens.asp?sitearea=PED American Cancer Society]
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*[http://www.cancer-carcinogen.info Information on Carcinogens]
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*[http://www.articleworld.org/index.php/Carcinogen Kinds of carcinogens]
 
{{Tumors}}
 
{{Tumors}}
  
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[[Category:Life sciences]]
 
[[Category:Life sciences]]

Revision as of 11:45, 2 August 2007


The term carcinogen refers to any substance, radionuclide or radiation which is an agent directly involved in the promotion of cancer or in the facilitation of its propagation. This may be due to genomic instability or to the disruption of cellular metabolic processes. Several radioactive substances are considered carcinogens, but their carcinogenic activity is attributed to the radiation, for example gamma rays or alpha particles, which they emit. Common examples of carcinogens are inhaled asbestos and tobacco smoke.

Carcinogenity

Cancer is a disease where damaged cells of the patient's body do not undergo programmed cell death, but their growth is no longer controlled and their metabolism is altered. Carcinogens may increase the risk of getting cancer by altering cellular metabolism or damaging DNA directly in cells, which interferes with biological processes, and induces the uncontrolled, malignant division ultimately leading to the formation of tumors. Usually DNA damage, if too severe to repair, leads to programmed cell death, but if the programmed cell death pathway is damaged, then the cell cannot prevent itself from becoming a cancer cell.

There are many natural carcinogens. Aflatoxin B1, which is produced by the fungus Aspergillus flavus growing on stored grains, nuts and peanut butter, is an example of a potent, naturally-occurring microbial carcinogen. Certain viruses such as Hepatitis B and human papilloma viruses have been found to cause cancer in humans. The first one shown to cause cancer in animals was Rous sarcoma virus, discovered in 1910 by Peyton Rous.

Benzene, kepone, EDB, asbestos, and the waste rock of oil shale mining have all been classified as carcinogenic.[citation needed] As far back as the 1930s, industrial and tobacco smoke were identified as sources of dozens of carcinogens, including benzopyrene, tobacco-specific nitrosamines such as nitrosonornicotine, and reactive aldehydes such as formaldehyde — which is also a hazard in embalming and making plastics. Vinyl chloride, from which PVC is manufactured, is a carcinogen and thus a hazard in PVC production.

Co-carcinogens are chemicals which do not separately cause cancer, but do so in specific combinations.

DNA is nucleophilic, therefore soluble carbon electrophiles are carcinogenic, because DNA attacks them. For example, some alkenes are toxicated by human enzymes to produce an electrophilic epoxide. DNA attacks the epoxide, and is bound permanently to it. This is the mechanism behind the carcinogenity of benzopyrene in tobacco smoke, other aromatics, aflatoxin and mustard gas.

After the carcinogen enters the body, the body makes an attempt to eliminate it through a process called biotransformation. The purpose of these reactions is to make the carcinogen more water-soluble so that it can be removed from the body. But these reactions can also convert a less toxic carcinogen into a more toxic one.

Radiation

CERCLA identifies all radionuclides as carcinogens, although the nature of the emitted radiation (alpha, beta, or gamma, and the energy), its consequent capacity to cause ionization in tissues, and the magnitude of radiation exposure, determine the potential hazard. For example, Thorotrast, a (incidentally-radioactive) suspension previously used as a contrast medium in x-ray diagnostics, is thought by some to be the most potent human carcinogen known because of its retention within various organs and persistent emission of alpha particles. Both Wilhelm Röntgen and Marie Curie died of cancer caused by radiation exposure during their experiments.

Not all types of electromagnetic radiation are carcinogenic. Low-energy waves on the electromagnetic spectrum are generally not, including radio waves, microwave radiation, infrared radiation, and visible light. Higher-energy radiation, including ultraviolet radiation (present in sunlight), x-rays, and gamma radiation, generally is carcinogenic, if received in sufficient doses.

Carcinogens in prepared food

Cooking food at high temperatures, for example broiling or barbecuing meats, can lead to the formation of minute quantities of many potent carcinogens that are comparable to those found in cigarette smoke (i.e., benzopyrene).[1] Charring of food resembles coking and tobacco pyrolysis and produces similar carcinogens. There are several carcinogenic pyrolysis products, such as polynuclear aromatic hydrocarbons, which are converted by human enzymes into epoxides, which attach permanently to DNA. Pre-cooking meats in a microwave oven for 2-3 minutes before broiling shortens the time on the hot pan, which can help minimize the formation of these carcinogens.

Recent reports have found that the known animal carcinogen acrylamide is generated in fried or overheated carbohydrate foods (such as french fries and potato chips). Studies are underway at the FDA and European regulatory agencies to assess its potential risk to humans. The charred residue on barbecued meats has been identified as a carcinogen, along with many other tars.

Nevertheless, the fact that the food contains minute quantities doesn't necessarily mean that there is a significant hazard. The gastrointestinal tract sheds its outer layer continuously to protect itself from carcinomas, and has a high activity of detoxifying enzymes. The lungs are not protected in this manner, therefore smoking is much more hazardous.

Classification of carcinogens

Carcinogens can be classified as genotoxic or nongenotoxic. Genotoxins cause irreversible genetic damage or mutations by binding to DNA. Genotoxins include chemical agents like N-Nitroso-N-Methylurea (MNU) or non-chemical agents such as ultraviolet light and ionizing radiation. Certain viruses can also act as carcinogens by interacting with DNA.

Nongenotoxins do not directly affect DNA but act in other ways to promote growth. These include hormones and some organic compounds.[2]

IARC classification of carcinogens

  • Group 1: the agent (mixture) is definitely carcinogenic to humans. The exposure circumstance entails exposures that are carcinogenic to humans.
  • Group 2A: the agent (mixture) is probably carcinogenic to humans. The exposure circumstance entails exposures that are probably carcinogenic to humans.
  • Group 2B: the agent (mixture) is possibly carcinogenic to humans. The exposure circumstance entails exposures that are possibly carcinogenic to humans.
  • Group 3: the agent (mixture or exposure circumstance) is not classifiable as to its carcinogenicity to humans.
  • Group 4: the agent (mixture) is probably not carcinogenic to humans.

Further details can be found in the IARC Monographs.

Notes

  1. ↑ Wei Zheng, Deborah R Gustafson, Rashmi Sinha, James R Cerhan, et al. "Well-done meat intake and the risk of breast cancer." Journal of the National Cancer Institute. Oxford: Nov 18, 1998.Vol. 90, Iss. 22; pg. 1724, 6 pgs.
  2. ↑ "The Gale Encyclopedia of Cancer: A guide to Cancer and its Treatments, Second Edition. Page no. 137".

See also

  • International Agency for Research on Cancer
  • Mutagen
  • Teratogen
  • Warburg's hypothesis

External links

Tumors (and related structures), Cancer, and Oncology
Benign - Premalignant - Carcinoma in situ - Malignant

Topography: Anus - Bladder - Bone - Brain - Breast - Cervix - Colon/rectum - Duodenum - Endometrium - Esophagus - Eye - Gallbladder - Head/Neck - Liver - Larynx - Lung - Mouth - Pancreas - Penis - Prostate - Kidney - Ovaries - Skin - Stomach - Testicles - Thyroid

Morphology: Papilloma/carcinoma - Adenoma/adenocarcinoma - Soft tissue sarcoma - Melanoma - Fibroma/fibrosarcoma - Lipoma/liposarcoma - Leiomyoma/leiomyosarcoma - Rhabdomyoma/rhabdomyosarcoma - Mesothelioma - Angioma/angiosarcoma - Osteoma/osteosarcoma - Chondroma/chondrosarcoma - Glioma - Lymphoma/leukemia

Treatment: Chemotherapy - Radiation therapy - Immunotherapy - Experimental cancer treatment

Related structures: Cyst - Dysplasia - Hamartoma - Neoplasia - Nodule - Polyp - Pseudocyst

Misc: Tumor suppressor genes/oncogenes - Staging/grading - Carcinogenesis/metastasis - Carcinogen - Research - Paraneoplastic phenomenon - ICD-O - List of oncology-related terms


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