Carcinogen

{{Main|radiation-induced cancer}}

CERCLA identifies all radionuclides as carcinogens, although the nature of the emitted radiation (alpha, beta, gamma, or neutron and the radioactive strength), its consequent capacity to cause ionization in tissues, and the magnitude of radiation exposure, determine the potential hazard. Carcinogenicity of radiation depends on the type of radiation, type of exposure, and penetration. For example, alpha radiation has low penetration and is not a hazard outside the body, but emitters are carcinogenic when inhaled or ingested. For example, Thorotrast, a (incidentally radioactive) suspension previously used as a contrast medium in x-ray diagnostics, is a potent human carcinogen known because of its retention within various organs and persistent emission of alpha particles. Low-level ionizing radiation may induce irreparable DNA damage (leading to replicational and transcriptional errors needed for neoplasia or may trigger viral interactions) leading to pre-mature aging and cancer.{{cite conference | vauthors = Acharya PV | title = The effect of ionizing radiation on the formation of age-correlated oligo deoxyribo nucleo phospheryl peptides in mammalian cells. | conference = 10th International Congress of Gerontology | location = Jerusalem | date = January 1975 }}{{cite conference | vauthors = Acharya PV | title = Implications of The Action of Low-Level Ionizing Radiation on the Inducement of Irreparable DNA Damage Leading to Mammalian Aging and Chemical Carcinogenesis. | conference = 10th International Congress of Biochemistry | location = Hamburg, Germany | date = July 1976 }}{{cite conference | vauthors = Acharya PV | title = Irreparable DNA-Damage by Industrial Pollutants in Pre-mature Aging, Chemical Carcinogenesis, and Cardiac Hypertrophy: Experiments and Theory | conference = 1st International Meeting of Heads of Clinical Biochemistry Laboratories | location = Jerusalem, Israel | date = April 1977 }}

Not all types of electromagnetic radiation are carcinogenic. Low-energy waves on the electromagnetic spectrum including radio waves, microwaves, infrared radiation and visible light are thought not to be, because they have insufficient energy to break chemical bonds. Evidence for carcinogenic effects of non-ionizing radiation is generally inconclusive, though there are some documented cases of radar technicians with prolonged high exposure experiencing significantly higher cancer incidence.{{cite journal | vauthors = Richter E, Berman T, Ben-Michael E, Laster R, Westin JB | title = Cancer in radar technicians exposed to radiofrequency/microwave radiation: sentinel episodes | journal = International Journal of Occupational and Environmental Health | volume = 6 | issue = 3 | pages = 187–193 | year = 2000 | pmid = 10926722 | doi = 10.1179/oeh.2000.6.3.187 | s2cid = 25147479 }}

Higher-energy radiation, including ultraviolet radiation (present in sunlight) generally is carcinogenic, if received in sufficient doses. For most people, ultraviolet radiations from sunlight is the most common cause of skin cancer. In Australia, where people with pale skin are often exposed to strong sunlight, melanoma is the most common cancer diagnosed in people aged 15–44 years.{{cite web|url=http://www.cancer.org.au/cancersmartlifestyle/SunSmart/Skincancerfactsandfigures.htm|title=Skin Cancer Facts and Figures|access-date=2010-07-02|archive-date=2012-08-10|archive-url=https://web.archive.org/web/20120810071104/http://www.cancer.org.au/cancersmartlifestyle/SunSmart/Skincancerfactsandfigures.htm|url-status=dead}}{{cite web| url = https://www.newscientist.com/article/dn13922-skintone-gene-could-predict-cancer-risk.html| title = Skin-tone gene could predict cancer risk}}

Substances or foods irradiated with electrons or electromagnetic radiation (such as microwave, X-ray or gamma) are not carcinogenic.{{cite web |author1=Center for Food Safety and Applied Nutrition |author1-link=Center for Food Safety and Applied Nutrition |title=Food Irradiation: What You Need to Know |url=https://www.fda.gov/food/buy-store-serve-safe-food/food-irradiation-what-you-need-know |website=FDA |access-date=20 January 2021 |language=en |date=20 April 2020}} In contrast, non-electromagnetic neutron radiation produced inside nuclear reactors can produce secondary radiation through nuclear transmutation.

{{main|Alcohol and cancer}}

Alcohol is a carcinogen of the head and neck, esophagus, liver, colon and rectum, and breast. It has a synergistic effect with tobacco smoke in the development of head and neck cancers. In the United States approximately 6% of cancers and 4% of cancer deaths are attributable to alcohol use.{{Cite web |title=Alcohol Use and Cancer |url=https://www.cancer.org/cancer/risk-prevention/diet-physical-activity/alcohol-use-and-cancer.html |access-date=2024-04-17 |website=www.cancer.org |language=en}}

Chemicals used in processed and cured meat such as some brands of bacon, sausages and ham may produce carcinogens.{{cite news |url=https://www.bbc.co.uk/news/health-34615621 |title=Processed meats do cause cancer - WHO|date= 26 October 2015 |work=BBC }} For example, nitrites used as food preservatives in cured meat such as bacon have also been noted as being carcinogenic with demographic links, but not causation, to colon cancer.{{cite journal | vauthors = Scanlan RA | title = Formation and occurrence of nitrosamines in food | journal = Cancer Research | volume = 43 | issue = 5 Suppl | pages = 2435s–2440s | date = May 1983 | pmid = 6831466 }}

{{See also|Cooking#Carcinogens|Raw foodism}}

Cooking food at high temperatures, for example grilling or barbecuing meats, may also lead to the formation of minute quantities of many potent carcinogens that are comparable to those found in cigarette smoke (i.e., benzo[a]pyrene).{{cite journal | vauthors = Zheng W, Gustafson DR, Sinha R, Cerhan JR, Moore D, Hong CP, Anderson KE, Kushi LH, Sellers TA, Folsom AR | title = Well-done meat intake and the risk of breast cancer | journal = Journal of the National Cancer Institute | volume = 90 | issue = 22 | pages = 1724–1729 | date = November 1998 | pmid = 9827527 | doi = 10.1093/jnci/90.22.1724 | doi-access = free }} Charring of food looks like coking and tobacco pyrolysis, and produces 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 grilling shortens the time on the hot pan, and removes heterocyclic amine (HCA) precursors, which can help minimize the formation of these carcinogens.{{cite web|url=http://www.cancer.gov/cancertopics/factsheet/Risk/heterocyclic-amines |title=National Cancer Institute, 2004 analysis and recommendations |publisher=Cancer.gov |date=2004-09-15 |access-date=2010-09-22}}

Frying, grilling or broiling food at high temperatures, especially starchy foods, until a toasted crust is formed generates acrylamides. This discovery in 2002 led to international health concerns. Subsequent research has however found that it is not likely that the acrylamides in burnt or well-cooked food cause cancer in humans; Cancer Research UK categorizes the idea that burnt food causes cancer as a "myth".{{cite web |url=https://www.cancerresearchuk.org/about-cancer/causes-of-cancer/cancer-myths/can-eating-burnt-foods-cause-cancer |publisher=Cancer Research UK |title=Can eating burnt foods cause cancer? |date=15 October 2021 }}

Several biologic agents are known carcinogens.

Aflatoxin B₁, a toxin produced by the fungus Aspergillus flavus which is a common contaminant of stored grains and nuts is a known cause of hepatocellular cancer. The bacteria H. Pylori is known to cause stomach cancer and MALT lymphoma.{{Cite web |last=cancer |first=Canadian Cancer Society / Société canadienne du |title=Helicobacter pylori |url=https://cancer.ca/en/cancer-information/reduce-your-risk/get-vaccinated/helicobacter-pylori |access-date=2024-04-17 |website=Canadian Cancer Society |language=en}} Hepatitis B and C are associated with the development of hepatocellular cancer. HPV is the primary cause of cervical cancer.

{{Main|Health effects of tobacco}}

Tobacco smoke contains at least 70 known carcinogens and is implicated in the development of numerous types of cancers including cancers of the lung, larynx, esophagus, stomach, kidney, pancreas, liver, bladder, cervix, colon, rectum and blood.{{Cite web |last=CDC |date=2019-08-27 |title=Cancer and Tobacco Use |url=https://www.cdc.gov/vitalsigns/cancerandtobacco/index.html |access-date=2024-04-17 |website=Centers for Disease Control and Prevention |language=en-us}} Potent carcinogens found in cigarette smoke include polycyclic aromatic hydrocarbons (PAH, such as benzo(a)pyrene), benzene, and nitrosamine.{{cite web |title=Harms of Cigarette Smoking and Health Benefits of Quitting |url=http://www.cancer.gov/about-cancer/causes-prevention/risk/tobacco/cessation-fact-sheet |work=National Cancer Institute |date=2017-12-21}}{{cite web |url = http://oehha.ca.gov/prop65/hazard_ident/pdf_zip/FinalMJsmokeHID.pdf | vauthors = Tomar RC, Beaumont J, Hsieh JC

|date = August 2009 |title = Evidence on the carcinogenicity of marijuana smoke |publisher = Reproductive and Cancer Hazard Assessment Branch Office of Environmental Health Hazard Assessment, California Environmental Protection Agency

|access-date = 23 June 2012 }}

Given that populations of workers are more likely to have consistent, often high level exposures to chemicals rarely encountered in normal life, much of the evidence for the carcinogenicity of specific agents is derived from studies of workers.

Selected carcinogens

• Gasoline (contains aromatics)
• Lead and its compounds
• Alkylating antineoplastic agents (e.g., mechlorethamine)
• Styrene
• Other alkylating agents (e.g., dimethyl sulfate)
• Ultraviolet radiation from the sun and UV lamps
• Other ionizing radiation (X-rays, gamma rays, etc.)
• Low refining or unrefined mineral oils

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 (NMU) 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.{{cite book| title=The Gale Encyclopedia of Cancer: A guide to Cancer and its Treatments |edition=Second |page=137 }}

The International Agency for Research on Cancer (IARC) is an intergovernmental agency established in 1965, which forms part of the World Health Organization of the United Nations. It is based in Lyon, France. Since 1971 it has published a series of Monographs on the Evaluation of Carcinogenic Risks to Humans{{cite web|url=http://monographs.iarc.fr/ |title=IARC Monographs |publisher=Monographs.iarc.fr |access-date=2010-09-22}} that have been highly influential in the classification of possible carcinogens.

• Group 1: the agent (mixture) is carcinogenic to humans. The exposure circumstance entails exposures that are carcinogenic to humans.
• Group 2A: the agent (mixture) is most likely (product more likely to be) carcinogenic to humans. The exposure circumstance entails exposures that are probably carcinogenic to humans.
• Group 2B: the agent (mixture) is possibly (chance of product being) 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 most likely not carcinogenic to humans.

The Globally Harmonized System of Classification and Labelling of Chemicals (GHS) is a United Nations initiative to attempt to harmonize the different systems of assessing chemical risk which currently exist (as of March 2009) around the world. It classifies carcinogens into two categories, of which the first may be divided again into subcategories if so desired by the competent regulatory authority:

• Category 1: known or presumed to have carcinogenic potential for humans
• Category 1A: the assessment is based primarily on human evidence
• Category 1B: the assessment is based primarily on animal evidence
• Category 2: suspected human carcinogens

The National Toxicology Program of the U.S. Department of Health and Human Services is mandated to produce a biennial Report on Carcinogens.Section 301(b)(4) of the Public Health Service Act, as amended by Section 262, Pub. L. 95–622. As of August 2024, the latest edition was the 15th report (2021).{{cite book | title = Report on Carcinogens | date = 2021 | edition = Fifteenth| publisher = U.S. Department of Health and Human Services, Public Health Service, National Toxicology Program | url = https://ntp.niehs.nih.gov/whatwestudy/assessments/cancer/roc | archive-url=http://web.archive.org/web/20240812000000/https://ntp.niehs.nih.gov/whatwestudy/assessments/cancer/roc | archive-date = 12 August 2024 }} It classifies carcinogens into two groups:

• Known to be a human carcinogen
• Reasonably anticipated to be a human carcinogen

The American Conference of Governmental Industrial Hygienists (ACGIH) is a private organization best known for its publication of threshold limit values (TLVs) for occupational exposure and monographs on workplace chemical hazards. It assesses carcinogenicity as part of a wider assessment of the occupational hazards of chemicals.

• Group A1: Confirmed human carcinogen
• Group A2: Suspected human carcinogen
• Group A3: Confirmed animal carcinogen with unknown relevance to humans
• Group A4: Not classifiable as a human carcinogen
• Group A5: Not suspected as a human carcinogen

The European Union classification of carcinogens is contained in the Regulation (EC) No 1272/2008. It consists of three categories:{{Cite web |url=https://echa.europa.eu/documents/10162/13562/cmr_report_en.pdf |title = CMR substances from Annex VI of the CLP Regulation | publisher = European Chemicals Agency | date = May 2012 |access-date=2020-11-03 |archive-date=2021-02-24 |archive-url=https://web.archive.org/web/20210224221346/https://echa.europa.eu/documents/10162/13562/cmr_report_en.pdf |url-status=dead }}

• Category 1A: Carcinogenic
• Category 1B: May cause cancer
• Category 2: Suspected of causing cancer

The former European Union classification of carcinogens was contained in the Dangerous Substances Directive and the Dangerous Preparations Directive. It also consisted of three categories:

• Category 1: Substances known to be carcinogenic to humans.
• Category 2: Substances which should be regarded as if they are carcinogenic to humans.
• Category 3: Substances which cause concern for humans, owing to possible carcinogenic effects but in respect of which the available information is not adequate for making a satisfactory assessment.

This assessment scheme is being phased out in favor of the GHS scheme (see above), to which it is very close in category definitions.

Under a previous name, the NOHSC, in 1999 Safe Work Australia published the Approved Criteria for Classifying Hazardous Substances [NOHSC:1008(1999)].{{cite web | url = http://www.safeworkaustralia.gov.au/AboutSafeWorkAustralia/WhatWeDo/Publications/Documents/504/Approved_Criteria_classifying_Hazardous_Substances_NOHSC1008_1999_2nd_Edition.pdf | work = Safe Work Australia | archive-url = https://web.archive.org/web/20101201103328/http://safeworkaustralia.gov.au/AboutSafeWorkAustralia/WhatWeDo/Publications/Documents/504/Approved_Criteria_classifying_Hazardous_Substances_NOHSC1008_1999_2nd_Edition.pdf |archive-date=2010-12-01 |url-status=dead |date= April 1999 | publisher = National Occupational Health and Safety Commission (NOHSC) | title = Approved criteria for classifying hazardous substances NOHSC:1008 (1999) }}

Section 4.76 of this document outlines the criteria for classifying carcinogens as approved by the Australian government. This classification consists of three categories:

• Category 1: Substances known to be carcinogenic to humans.
• Category 2: Substances that should be regarded as if they were carcinogenic to humans.
• Category 3: Substances that have possible carcinogenic effects in humans but about which there is insufficient information to make an assessment.

In this section, the carcinogens implicated as the main causative agents of the four most common cancers worldwide are briefly described. These four cancers are lung, breast, colon, and stomach cancers. Together they account for about 41% of worldwide cancer incidence and 42% of cancer deaths (for more detailed information on the carcinogens implicated in these and other cancers, see references{{cite book | vauthors = Bernstein H, Payne CM, Bernstein C, Garewal H, Dvorak K | date = 2008 | chapter = Cancer and aging as consequences of un-repaired DNA damage. | title = New Research on DNA Damages | veditors = Kimura H, Suzuki A | publisher = Nova Science Publishers, Inc. | location = New York | pages = 1–47 | chapter-url = https://www.novapublishers.com/catalog/product_info.php?products_id=43247 | archive-url = https://web.archive.org/web/20141025091740/https://www.novapublishers.com/catalog/product_info.php?products_id=43247 | archive-date=2014-10-25 | isbn = 978-1-60456-581-2}}).

Lung cancer (pulmonary carcinoma) is the most common cancer in the world, both in terms of cases (1.6 million cases; 12.7% of total cancer cases) and deaths (1.4 million deaths; 18.2% of total cancer deaths).{{cite journal | vauthors = Ferlay J, Shin HR, Bray F, Forman D, Mathers C, Parkin DM | title = Estimates of worldwide burden of cancer in 2008: GLOBOCAN 2008 | journal = International Journal of Cancer | volume = 127 | issue = 12 | pages = 2893–2917 | date = December 2010 | pmid = 21351269 | doi = 10.1002/ijc.25516 | s2cid = 23583962 | doi-access = free }} Lung cancer is largely caused by tobacco smoke. Risk estimates for lung cancer in the United States indicate that tobacco smoke is responsible for 90% of lung cancers. Other factors are implicated in lung cancer, and these factors can interact synergistically with smoking so that total attributable risk adds up to more than 100%. These factors include occupational exposure to carcinogens (about 9-15%), radon (10%) and outdoor air pollution (1-2%).{{cite journal | vauthors = Alberg AJ, Ford JG, Samet JM | title = Epidemiology of lung cancer: ACCP evidence-based clinical practice guidelines (2nd edition) | journal = Chest | volume = 132 | issue = 3 Suppl | pages = 29S–55S | date = September 2007 | pmid = 17873159 | doi = 10.1378/chest.07-1347 }}

Tobacco smoke is a complex mixture of more than 5,300 identified chemicals. The most important carcinogens in tobacco smoke have been determined by a "Margin of Exposure" approach.{{cite journal | vauthors = Cunningham FH, Fiebelkorn S, Johnson M, Meredith C | title = A novel application of the Margin of Exposure approach: segregation of tobacco smoke toxicants | journal = Food and Chemical Toxicology | volume = 49 | issue = 11 | pages = 2921–2933 | date = November 2011 | pmid = 21802474 | doi = 10.1016/j.fct.2011.07.019 }} Using this approach, the most important tumorigenic compounds in tobacco smoke were, in order of importance, acrolein, formaldehyde, acrylonitrile, 1,3-butadiene, cadmium, acetaldehyde, ethylene oxide, and isoprene. Most of these compounds cause DNA damage by forming DNA adducts or by inducing other alterations in DNA.{{Citation needed|date=December 2019|reason=removed citation to book from predatory publisher}} DNA damages are subject to error-prone DNA repair or can cause replication errors. Such errors in repair or replication can result in mutations in tumor suppressor genes or oncogenes leading to cancer.

Breast cancer is the second most common cancer [(1.4 million cases, 10.9%), but ranks 5th as cause of death (458,000, 6.1%)]. Increased risk of breast cancer is associated with persistently elevated blood levels of estrogen.{{cite journal | vauthors = Yager JD, Davidson NE | title = Estrogen carcinogenesis in breast cancer | journal = The New England Journal of Medicine | volume = 354 | issue = 3 | pages = 270–282 | date = January 2006 | pmid = 16421368 | doi = 10.1056/NEJMra050776 | s2cid = 5793142 }} Estrogen appears to contribute to breast carcinogenesis by three processes; (1) the metabolism of estrogen to genotoxic, mutagenic carcinogens, (2) the stimulation of tissue growth, and (3) the repression of phase II detoxification enzymes that metabolize ROS leading to increased oxidative DNA damage.{{cite journal | vauthors = Ansell PJ, Espinosa-Nicholas C, Curran EM, Judy BM, Philips BJ, Hannink M, Lubahn DB | title = In vitro and in vivo regulation of antioxidant response element-dependent gene expression by estrogens | journal = Endocrinology | volume = 145 | issue = 1 | pages = 311–317 | date = January 2004 | pmid = 14551226 | doi = 10.1210/en.2003-0817 | doi-access = free }}{{cite journal | vauthors = Belous AR, Hachey DL, Dawling S, Roodi N, Parl FF | title = Cytochrome P450 1B1-mediated estrogen metabolism results in estrogen-deoxyribonucleoside adduct formation | journal = Cancer Research | volume = 67 | issue = 2 | pages = 812–817 | date = January 2007 | pmid = 17234793 | doi = 10.1158/0008-5472.CAN-06-2133 | s2cid = 24602808 | doi-access = }}{{cite journal | vauthors = Bolton JL, Thatcher GR | title = Potential mechanisms of estrogen quinone carcinogenesis | language = EN | journal = Chemical Research in Toxicology | volume = 21 | issue = 1 | pages = 93–101 | date = January 2008 | pmid = 18052105 | pmc = 2556295 | doi = 10.1021/tx700191p }}

The major estrogen in humans, estradiol, can be metabolized to quinone derivatives that form adducts with DNA.{{cite journal | vauthors = Yue W, Santen RJ, Wang JP, Li Y, Verderame MF, Bocchinfuso WP, Korach KS, Devanesan P, Todorovic R, Rogan EG, Cavalieri EL | title = Genotoxic metabolites of estradiol in breast: potential mechanism of estradiol induced carcinogenesis | journal = The Journal of Steroid Biochemistry and Molecular Biology | volume = 86 | issue = 3–5 | pages = 477–486 | date = September 2003 | pmid = 14623547 | doi = 10.1016/s0960-0760(03)00377-7 | s2cid = 31885800 }} These derivatives can cause depurination, the removal of bases from the phosphodiester backbone of DNA, followed by inaccurate repair or replication of the apurinic site leading to mutation and eventually cancer. This genotoxic mechanism may interact in synergy with estrogen receptor-mediated, persistent cell proliferation to ultimately cause breast cancer. Genetic background, dietary practices and environmental factors also likely contribute to the incidence of DNA damage and breast cancer risk.

Consumption of alcohol has also been linked to an increased risk for breast cancer.{{cite journal | vauthors = McDonald JA, Goyal A, Terry MB | title = Alcohol Intake and Breast Cancer Risk: Weighing the Overall Evidence | journal = Current Breast Cancer Reports | volume = 5 | issue = 3 | pages = 208–221 | date = September 2013 | pmid = 24265860 | pmc = 3832299 | doi = 10.1007/s12609-013-0114-z }}

Colorectal cancer is the third most common cancer [1.2 million cases (9.4%), 608,000 deaths (8.0%)]. Tobacco smoke may be responsible for up to 20% of colorectal cancers in the United States.{{cite journal | vauthors = Giovannucci E, Martínez ME | title = Tobacco, colorectal cancer, and adenomas: a review of the evidence | journal = Journal of the National Cancer Institute | volume = 88 | issue = 23 | pages = 1717–1730 | date = December 1996 | pmid = 8944002 | doi = 10.1093/jnci/88.23.1717 | doi-access = }} In addition, substantial evidence implicates bile acids as an important factor in colon cancer. Twelve studies (summarized in Bernstein et al.{{cite journal | vauthors = Bernstein H, Bernstein C, Payne CM, Dvorak K | title = Bile acids as endogenous etiologic agents in gastrointestinal cancer | journal = World Journal of Gastroenterology | volume = 15 | issue = 27 | pages = 3329–3340 | date = July 2009 | pmid = 19610133 | pmc = 2712893 | doi = 10.3748/wjg.15.3329 | doi-access = free }}) indicate that the bile acids deoxycholic acid (DCA) or lithocholic acid (LCA) induce production of DNA-damaging reactive oxygen species or reactive nitrogen species in human or animal colon cells. Furthermore, 14 studies showed that DCA and LCA induce DNA damage in colon cells. Also 27 studies reported that bile acids cause programmed cell death (apoptosis).

Increased apoptosis can result in selective survival of cells that are resistant to induction of apoptosis. Colon cells with reduced ability to undergo apoptosis in response to DNA damage would tend to accumulate mutations, and such cells may give rise to colon cancer. Epidemiologic studies have found that fecal bile acid concentrations are increased in populations with a high incidence of colon cancer. Dietary increases in total fat or saturated fat result in elevated DCA and LCA in feces and elevated exposure of the colon epithelium to these bile acids. When the bile acid DCA was added to the standard diet of wild-type mice invasive colon cancer was induced in 56% of the mice after 8 to 10 months.{{cite journal | vauthors = Bernstein C, Holubec H, Bhattacharyya AK, Nguyen H, Payne CM, Zaitlin B, Bernstein H | title = Carcinogenicity of deoxycholate, a secondary bile acid | journal = Archives of Toxicology | volume = 85 | issue = 8 | pages = 863–871 | date = August 2011 | pmid = 21267546 | pmc = 3149672 | doi = 10.1007/s00204-011-0648-7 | bibcode = 2011ArTox..85..863B }} Overall, the available evidence indicates that DCA and LCA are centrally important DNA-damaging carcinogens in colon cancer.

Stomach cancer is the fourth most common cancer [990,000 cases (7.8%), 738,000 deaths (9.7%)]. Helicobacter pylori infection is the main causative factor in stomach cancer. Chronic gastritis (inflammation) caused by H. pylori is often long-standing if not treated. Infection of gastric epithelial cells with H. pylori results in increased production of reactive oxygen species (ROS).{{cite journal | vauthors = Ding SZ, Minohara Y, Fan XJ, Wang J, Reyes VE, Patel J, Dirden-Kramer B, Boldogh I, Ernst PB, Crowe SE | title = Helicobacter pylori infection induces oxidative stress and programmed cell death in human gastric epithelial cells | journal = Infection and Immunity | volume = 75 | issue = 8 | pages = 4030–4039 | date = August 2007 | pmid = 17562777 | pmc = 1952011 | doi = 10.1128/IAI.00172-07 }}{{cite journal | vauthors = Handa O, Naito Y, Yoshikawa T | title = Redox biology and gastric carcinogenesis: the role of Helicobacter pylori | journal = Redox Report | volume = 16 | issue = 1 | pages = 1–7 | year = 2011 | pmid = 21605492 | pmc = 6837368 | doi = 10.1179/174329211X12968219310756 | doi-access = free }} ROS cause oxidative DNA damage including the major base alteration 8-hydroxydeoxyguanosine (8-OHdG). 8-OHdG resulting from ROS is increased in chronic gastritis. The altered DNA base can cause errors during DNA replication that have mutagenic and carcinogenic potential. Thus H. pylori-induced ROS appear to be the major carcinogens in stomach cancer because they cause oxidative DNA damage leading to carcinogenic mutations.

Diet is also thought to be a contributing factor in stomach cancer: in Japan, where very salty pickled foods are popular, the incidence of stomach cancer is high. Preserved meat such as bacon, sausages, and ham increases the risk, while a diet rich in fresh fruit, vegetables, peas, beans, grains, nuts, seeds, herbs, and spices will reduce the risk. The risk also increases with age.{{cite web |url=http://www.cancerresearchuk.org/about-cancer/type/stomach-cancer/about/stomach-cancer-risks-and-causes |title=Stomach cancer risks and causes |work=Cancer Research UK }}

{{Columns-list|colwidth=30em|

• History of cancer
• Mutagen
• Possible carcinogen
• Safe handling of carcinogens
• Teratology

}}

{{Reflist|30em}}

{{Wiktionary|carcinogen}}

{{Commons category|Carcinogens}}

• {{cite web | url = https://www.cdc.gov/niosh/topics/cancer/npotocca.html | title = Occupational Cancer - Carcinogen List | publisher = CDC | work = NIOSH Workplace Safety & Health |date= May 2, 2012 |url-status=dead |archive-url= https://web.archive.org/web/20230530104021/https://www.cdc.gov/niosh/topics/cancer/npotocca.html |archive-date= May 30, 2023 }}
• {{cite web | title=IARC Monographs on the Identification of Carcinogenic Hazards to Humans | website=International Agency for Research on Cancer | url=https://monographs.iarc.who.int/}}
• {{cite web | title = Known and Probable Carcinogens | url = http://www.cancer.org/docroot/PED/content/PED_1_3x_Known_and_Probable_Carcinogens.asp?sitearea=PED | work = American Cancer Society |date=2006 | archive-url=https://web.archive.org/web/20080317051133/http://www.cancer.org/docroot/PED/content/PED_1_3x_Known_and_Probable_Carcinogens.asp?sitearea=PED | archive-date=2008-03-17 }}
• {{cite web | title = Recognized Carcinogens | url = http://www.scorecard.org/health-effects/chemicals.tcl?short_hazard_name=cancer&all_p=t |website=Scorecard | archive-url = https://web.archive.org/web/20071217104833/http://www.scorecard.org/health-effects/chemicals.tcl?short_hazard_name=cancer&all_p=t | archive-date=2007-12-17 }}
• {{cite web | url = http://ntp.niehs.nih.gov/index.cfm?objectid=03C9B512-ACF8-C1F3-ADBA53CAE848F635 | work = U.S. National Toxicology Program | title = Report on Carcinogens | access-date = 2018-08-08 | archive-date = 2005-10-28 | archive-url = https://web.archive.org/web/20051028174523/http://ntp.niehs.nih.gov/index.cfm?objectid=03C9B512-ACF8-C1F3-ADBA53CAE848F635 | url-status = dead |date=2005 }}

{{Carcinogen|state=uncollapsed}}

{{Tumors}}

{{Toxicology}}

{{Genotoxicity}}

{{HealthIssuesOfPlastics}}

{{Authority control}}

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Category:Radiation health effects

Category:Occupational safety and health