Editing Carcinogen (section)

{{Short description|Substance, radionuclide, or radiation directly involved in causing cancer}}
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| footer = Common carcinogens; clockwise from top left: [[tobacco smoking]], [[alcohol and cancer|alcohol]], [[asbestos]], [[ultraviolet]] radiation
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A '''carcinogen''' ({{IPAc-en|k|ɑːr|ˈ|s|ɪ|n|ə|dʒ|ən}}) is any agent that promotes the development of [[cancer]].<ref name=":1">{{Cite web |title=Carcinogen |url=https://www.genome.gov/genetics-glossary/Carcinogen |access-date=2024-04-16 |website=www.genome.gov |language=en}}</ref>   Carcinogens can include [[synthetic chemical]]s, naturally occurring substances, physical agents such as ionizing and non-ionizing [[radiation]], and [[Biological agent|biologic agents]] such as viruses and [[carcinogenic bacteria|bacteria]].<ref name=":2" />  Most carcinogens act by creating mutations in [[DNA]] that disrupt a cell's normal processes for regulating growth, leading to uncontrolled cellular proliferation.<ref name=":1" /> This occurs when the cell's [[DNA repair]] processes fail to identify DNA damage allowing the defect to be passed down to [[daughter cells]]. The damage accumulates over time. This is typically a multi-step process during which the regulatory mechanisms within the cell are gradually dismantled allowing for unchecked [[Cell division|cellular division]].<ref name=":2">{{Cite web |title=Carcinogenesis |url=https://hemonc.mhmedical.com/content.aspx?sectionid=253777560&bookid=3022 |access-date=2024-04-16 |website=McGraw Hill Medical |language=en}}</ref>

The specific mechanisms for carcinogenic activity is unique to each agent and cell type. Carcinogens can be broadly categorized, however,  as activation-dependent and activation-independent which relate to the agent's ability to engage directly with DNA.<ref name=":0">{{cite journal |vauthors=Barnes JL, Zubair M, John K, Poirier MC, Martin FL |date=October 2018 |title=Carcinogens and DNA damage |journal=Biochemical Society Transactions |volume=46 |issue=5 |pages=1213–1224 |doi=10.1042/bst20180519 |pmc=6195640 |pmid=30287511}}</ref> Activation-dependent agents are relatively inert in their original form, but are bioactivated in the body into [[metabolite]]s or intermediaries capable of damaging human DNA.<ref name=":4">{{Cite journal |url=https://portlandpress.com/biochemsoctrans/article/46/5/1213/67954/Carcinogens-and-DNA-damage |access-date=2024-04-17 |journal=Biochemical Society Transactions |doi=10.1042/bst20180519 |pmc=6195640 |pmid=30287511 |title=Carcinogens and DNA damage |date=2018 |last1=Barnes |first1=Jessica L. |last2=Zubair |first2=Maria |last3=John |first3=Kaarthik |last4=Poirier |first4=Miriam C. |last5=Martin |first5=Francis L. |volume=46 |issue=5 |pages=1213–1224 }}</ref> These are also known as "indirect-acting" carcinogens. Examples of activation-dependent carcinogens include [[polycyclic aromatic hydrocarbon]]s (PAHs), [[heterocyclic aromatic amine]]s, and [[mycotoxin]]s. Activation-independent carcinogens, or "direct-acting" carcinogens, are those that are capable of directly damaging DNA without any modification to their molecular structure. These agents typically include [[Electrophile|electrophilic]] groups that react readily with the net negative charge of DNA molecules.<ref name=":0" /> Examples of  activation-independent carcinogens include [[Ultraviolet|ultraviolet light]], [[ionizing radiation]] and [[alkylating agent]]s.<ref name=":4" />

The time from exposure to a carcinogen to the development of cancer is known as the [[latency period]]. For most solid tumors in humans the latency period is between 10 and 40 years depending on cancer type.<ref name=":3">{{Cite book |last1=Ladou |last2=Harrison |title=Current Diagnosis and Treatment Occupational and Environmental Medicine |publisher=McGraw Hill Lange |year=2014 |isbn=978-1-260-14343-0 |edition=6th |pages=389–418}}</ref> For blood cancers, the latency period may be as short as two.<ref name=":3" /> Due to prolonged latency periods identification of carcinogens can be challenging.

A number of organizations review and evaluate the cumulative scientific evidence regarding the potential carcinogenicity of specific substances. Foremost among these is the [[International Agency for Research on Cancer]] (IARC). IARC routinely publishes monographs in which specific substances are evaluated for their potential carcinogenicity to humans and subsequently categorized into one of four groupings: Group 1: Carcinogenic to humans, Group 2A: Probably carcinogenic to humans, Group 2B:  Possibly carcinogenic to humans and Group 3: Not classifiable as to its carcinogenicity to humans.<ref>{{Cite web |title=IARC Monographs on the Identification of Carcinogenic Hazards to Humans|url=https://monographs.iarc.who.int/ |access-date=2024-04-17 |website=monographs.iarc.who.int |language=en-US}}</ref> Other organizations that evaluate the carcinogenicity of substances include the [[National Toxicology Program]] of the [[US Public Health Service]], [[NIOSH]], the [[American Conference of Governmental Industrial Hygienists]] and others.<ref>{{Cite web |title=Determining if Something Is a Carcinogen |url=https://www.cancer.org/cancer/risk-prevention/understanding-cancer-risk/determining-if-something-is-a-carcinogen.html |access-date=2024-04-17 |website=www.cancer.org |language=en}}</ref>

There are numerous sources of exposures to carcinogens including [[ultraviolet radiation]] from the sun, [[radon gas]]<ref>{{Cite web |last=CDC |date=2023-12-21 |title=Radon in the Home |url=https://www.cdc.gov/radon/radon-facts.html |access-date=2024-04-17 |website=Centers for Disease Control and Prevention |language=en-us}}</ref> emitted in residential basements, environmental contaminants such as [[chlordecone]], cigarette smoke and ingestion of some types of foods such as alcohol and [[processed meat]]s.<ref>{{Cite web |last=Underferth |first=Danielle |title=Processed meat and cancer: What you need to know |url=https://www.mdanderson.org/publications/focused-on-health/eat-less-processed-meat.h11-1590624.html |access-date=2024-04-17 |website=MD Anderson Cancer Center |language=en}}</ref> Occupational exposures represent a major source of carcinogens with an estimated 666,000 annual fatalities worldwide attributable to work related cancers.<ref name=":5">{{Cite journal |last1=Loomis |first1=Dana |last2=Guha |first2=Neela |last3=Hall |first3=Amy L |last4=Straif |first4=Kurt |date=August 2018 |title=Identifying occupational carcinogens: an update from the IARC Monographs |journal=Occupational and Environmental Medicine |language=en |volume=75 |issue=8 |pages=593–603 |doi=10.1136/oemed-2017-104944 |issn=1351-0711 |pmc=6204931 |pmid=29769352}}</ref> According to [[National Institute for Occupational Safety and Health|NIOSH]], 3-6% of cancers worldwide are due to occupational exposures.<ref name=":3" /> Well established occupational carcinogens include [[vinyl chloride]] and [[hemangiosarcoma]] of the liver, [[benzene]] and [[leukemia]], [[aniline dyes]] and [[bladder cancer]], [[asbestos]] and [[mesothelioma]], [[polycyclic aromatic hydrocarbon]]s and [[Chimney sweeps' carcinoma|scrotal cancer]] among chimney sweeps to name a few.