Editing Cancer (section)

== Causes ==
{{Main|Causes of cancer}}
[[File:GHS-pictogram-silhouette.svg|thumb|The GHS [[hazard symbol|Hazard pictogram]] for carcinogenic substances]]
[[File:Share-of-cancer-deaths-attributed-to-tobacco.png|thumb|upright=1.6|Share of cancer deaths attributed to tobacco in 2016.<ref>{{cite web |title=Share of cancer deaths attributed to tobacco |url=https://ourworldindata.org/grapher/share-of-cancer-deaths-attributed-to-tobacco |website=Our World in Data |access-date=5 March 2020}}</ref>]]
The majority of cancers, some 90–95% of cases, are due to genetic mutations from environmental and lifestyle factors.<ref name=Enviro2008/> The remaining 5–10% are due to [[Heredity|inherited genetics]].<ref name=Enviro2008/> ''[[Environment (biophysical)|Environmental]]'' refers to any cause that is not [[Heredity|inherited]], such as lifestyle, economic, and behavioral factors and not merely pollution.<ref name="isbn0-387-78192-7">{{cite book | vauthors = Manton K, Akushevich I, Kravchenko J |title=Cancer Mortality and Morbidity Patterns in the U.S. Population: An Interdisciplinary Approach |url={{google books |plainurl=y |id=fDIbuwtYPlAC}}|date=28 December 2008|publisher=Springer Science & Business Media|isbn=978-0-387-78193-8|quote = The term ''environment'' refers not only to air, water, and soil but also to substances and conditions at home and at the workplace, including diet, smoking, alcohol, drugs, exposure to chemicals, sunlight, ionizing radiation, electromagnetic fields, infectious agents, etc. Lifestyle, economic and behavioral factors are all aspects of our environment. }}</ref> Common environmental factors that contribute to cancer death include tobacco use (25–30%), diet and [[obesity]] (30–35%), infections (15–20%), [[radiation]] (both ionizing and non-ionizing, up to 10%), lack of [[physical exercise|physical activity]], and pollution.<ref name=Enviro2008/><ref>{{cite journal | vauthors = Islami F, Goding Sauer A, Miller KD, Siegel RL, Fedewa SA, Jacobs EJ, McCullough ML, Patel AV, Ma J, Soerjomataram I, Flanders WD, Brawley OW, Gapstur SM, Jemal A | title = Proportion and number of cancer cases and deaths attributable to potentially modifiable risk factors in the United States | journal = CA: A Cancer Journal for Clinicians | volume = 68 | issue = 1 | pages = 31–54 | date = January 2018 | pmid = 29160902 | doi = 10.3322/caac.21440 | doi-access = free }}</ref> Psychological stress does not appear to be a risk factor for the onset of cancer,<ref name=Cohen2019>{{cite journal | vauthors = Cohen S, Murphy ML, Prather AA | title = Ten Surprising Facts About Stressful Life Events and Disease Risk | journal = Annual Review of Psychology | volume = 70 | pages = 577–597 | date = January 2019 | pmid = 29949726 | pmc = 6996482 | doi = 10.1146/annurev-psych-010418-102857 | quote = the strongest conclusion derived from decades of research on stressors and cancer is that stressful events may be associated with decreased cancer survival but are probably not associated with disease incidence (Chida et al. 2008). }}</ref><ref name="pmid23393080">{{cite journal | vauthors = Heikkilä K, Nyberg ST, Theorell T, Fransson EI, Alfredsson L, Bjorner JB, Bonenfant S, Borritz M, Bouillon K, Burr H, Dragano N, Geuskens GA, Goldberg M, Hamer M, Hooftman WE, Houtman IL, Joensuu M, Knutsson A, Koskenvuo M, Koskinen A, Kouvonen A, Madsen IE, Magnusson Hanson LL, Marmot MG, Nielsen ML, Nordin M, Oksanen T, Pentti J, Salo P, Rugulies R, Steptoe A, Suominen S, Vahtera J, Virtanen M, Väänänen A, Westerholm P, Westerlund H, Zins M, Ferrie JE, Singh-Manoux A, Batty GD, Kivimäki M | title = Work stress and risk of cancer: meta-analysis of 5700 incident cancer events in 116,000 European men and women | journal = BMJ | volume = 346 | pages = f165 | date = February 2013 | pmid = 23393080 | pmc = 3567204 | doi = 10.1136/bmj.f165 }}</ref> though it may worsen outcomes in those who already have cancer.<ref name=Cohen2019/>

Environmental or lifestyle factors that caused cancer to develop in an individual can be identified by analyzing mutational signatures from genomic sequencing of tumor DNA. For example, this can reveal if lung cancer was caused by tobacco smoke, if skin cancer was caused by UV radiation, or if [[Secondary malignant neoplasm|secondary cancers]] were caused by previous chemotherapy treatment.<ref name=cds>{{cite journal | vauthors = Steele CD, Pillay N, Alexandrov LB | title = An overview of mutational and copy number signatures in human cancer | journal = The Journal of Pathology | volume = 257 | issue = 4 | pages = 454–465 | date = July 2022 | pmid = 35420163 | pmc = 9324981 | doi = 10.1002/path.5912 }}</ref>

Cancer is generally not a [[transmission (medicine)|transmissible disease]].<ref name=Tolar>{{cite journal |vauthors=Tolar J, Neglia JP |s2cid=34197973 |title=Transplacental and other routes of cancer transmission between individuals |journal=Journal of Pediatric Hematology/Oncology |volume=25 |issue=6 |pages=430–4 |date=June 2003 |pmid=12794519 |doi=10.1097/00043426-200306000-00002}}</ref> Exceptions include rare transmissions that occur with pregnancies and occasional [[Organ donation|organ donors]]. However, transmissible infectious diseases such as [[hepatitis B]], [[Epstein-Barr virus]], [[Human Papilloma Virus]] and [[HIV]], can contribute to the development of cancer.<ref>{{cite web |title=Hepatitis B virus (HBV) and hepatitis C virus (HCV) |url=https://www.cancer.org/cancer/risk-prevention/infections/infections-that-can-lead-to-cancer/viruses.html |website=American Cancer Society |access-date=15 February 2025}}</ref>

=== Chemicals ===
{{Further|Alcohol and cancer|Smoking and cancer}}
[[File:Cancer smoking lung cancer correlation from NIH.svg|thumb|upright=1.35|The incidence of lung cancer is highly correlated with smoking.]]
Exposure to particular substances have been linked to specific types of cancer. These substances are called ''[[carcinogen]]s''.

[[Tobacco smoking|Tobacco smoke]], for example, causes 90% of lung cancer.<ref name="pmid9594919">{{cite journal |vauthors=Biesalski HK, Bueno de Mesquita B, Chesson A, Chytil F, Grimble R, Hermus RJ, Köhrle J, Lotan R, Norpoth K, Pastorino U, Thurnham D |title=European Consensus Statement on Lung Cancer: risk factors and prevention. Lung Cancer Panel |journal=CA: A Cancer Journal for Clinicians |volume=48 |issue=3 |pages=167–76; discussion 164–66 |year=1998 |pmid=9594919 |doi=10.3322/canjclin.48.3.167|s2cid=20891885 |doi-access=free }}</ref> Tobacco use can cause cancer throughout the body including in the mouth and throat, [[larynx]], [[esophagus]], stomach, bladder, kidney, cervix, colon/rectum, liver and [[pancreas]].<ref name="pmid12270001">{{cite journal |vauthors=Kuper H, Boffetta P, Adami HO |s2cid=6132726 |title=Tobacco use and cancer causation: association by tumour type |journal=Journal of Internal Medicine |volume=252 |issue=3 |pages=206–24 |date=September 2002 |pmid=12270001 |doi=10.1046/j.1365-2796.2002.01022.x|doi-access=free }}</ref><ref>{{Cite web |date=27 August 2019 |title=Cancer and Tobacco Use |url=https://www.cdc.gov/vitalsigns/cancerandtobacco/index.html |access-date=25 October 2023 |website=Centers for Disease Control and Prevention |language=en-us}}</ref> Tobacco smoke contains over fifty known carcinogens, including [[nitrosamine]]s and [[polycyclic aromatic hydrocarbon]]s.<ref name=Kuper/>

Tobacco is responsible for about one in five cancer deaths worldwide<ref name="Kuper">{{cite journal |vauthors=Kuper H, Adami HO, Boffetta P |s2cid=9172672 |title=Tobacco use, cancer causation and public health impact |journal=Journal of Internal Medicine |volume=251 |issue=6 |pages=455–66 |date=June 2002 |pmid=12028500 |doi=10.1046/j.1365-2796.2002.00993.x|doi-access=free }}</ref> and about one in three in the developed world.<ref name="Sasco">{{cite journal |vauthors=Sasco AJ, Secretan MB, Straif K |title=Tobacco smoking and cancer: a brief review of recent epidemiological evidence |journal=Lung Cancer |volume=45 | issue = Suppl 2 |pages=S3–9 |date=August 2004 |pmid=15552776 |doi=10.1016/j.lungcan.2004.07.998}}</ref> 
Lung cancer death rates in the United States have mirrored [[tobacco smoking|smoking]] patterns, with increases in smoking followed by dramatic increases in lung cancer death rates and, more recently, decreases in smoking rates since the 1950s followed by decreases in lung cancer death rates in men since 1990.<ref name="pmid16998161">{{cite journal |vauthors=Thun MJ, Jemal A |title=How much of the decrease in cancer death rates in the United States is attributable to reductions in tobacco smoking? |journal=Tobacco Control |volume=15 |issue=5 |pages=345–47 |date=October 2006 |pmid=16998161 |pmc=2563648 |doi=10.1136/tc.2006.017749}}</ref><ref name="pmid18434333">{{cite journal |vauthors=Dubey S, Powell CA |title=Update in lung cancer 2007 |journal=American Journal of Respiratory and Critical Care Medicine |volume=177 |issue=9 |pages=941–46 |date=May 2008 |pmid=18434333 |pmc=2720127 |doi=10.1164/rccm.200801-107UP}}</ref>

Alcohol increases the risk of cancer of the breast (in women), throat, liver, oesophagus, mouth, larynx, and colon.<ref>{{cite news |title=US top doctor calls for cancer warnings on alcohol |url=https://www.bbc.com/news/articles/cj90x3np0zpo |agency=BBC}}</ref>
In Western Europe, 10% of cancers in males and 3% of cancers in females are attributed to alcohol exposure, especially liver and digestive tract cancers.<ref name="pmid21474525">{{cite journal |vauthors=Schütze M, Boeing H, Pischon T, Rehm J, Kehoe T, Gmel G, Olsen A, Tjønneland AM, Dahm CC, Overvad K, Clavel-Chapelon F, Boutron-Ruault MC, Trichopoulou A, Benetou V, Zylis D, Kaaks R, Rohrmann S, Palli D, Berrino F, Tumino R, Vineis P, Rodríguez L, Agudo A, Sánchez MJ, Dorronsoro M, Chirlaque MD, Barricarte A, Peeters PH, van Gils CH, Khaw KT, Wareham N, Allen NE, Key TJ, Boffetta P, Slimani N, Jenab M, Romaguera D, Wark PA, Riboli E, Bergmann MM |title=Alcohol attributable burden of incidence of cancer in eight European countries based on results from prospective cohort study |journal=BMJ |volume=342 |pages=d1584 |date=April 2011 |pmid=21474525 |pmc=3072472 |doi=10.1136/bmj.d1584}}</ref> Cancer from work-related substance exposures may cause between 2 and 20% of cases,<ref name="pmid18055160">{{cite journal |vauthors=Irigaray P, Newby JA, Clapp R, Hardell L, Howard V, Montagnier L, Epstein S, Belpomme D |title=Lifestyle-related factors and environmental agents causing cancer: an overview |journal=Biomedicine & Pharmacotherapy |volume=61 |issue=10 |pages=640–58 |date=December 2007 |pmid=18055160 |doi=10.1016/j.biopha.2007.10.006}}</ref> causing at least 200,000 deaths.<ref name="WHO_occup">{{cite press release |title=WHO calls for prevention of cancer through healthy workplaces |publisher=World Health Organization |date=27 April 2007 |url=https://www.who.int/mediacentre/news/notes/2007/np19/en/index.html |access-date=13 October 2007 |archive-url=https://web.archive.org/web/20071012202014/http://www.who.int/mediacentre/news/notes/2007/np19/en/index.html |archive-date=12 October 2007}}</ref> Cancers such as lung cancer and [[mesothelioma]] can come from inhaling tobacco smoke or [[asbestos]] fibers, or [[leukemia]] from exposure to [[benzene]].<ref name=WHO_occup/>

Exposure to [[perfluorooctanoic acid]] (PFOA), which is predominantly used in the production of [[Polytetrafluoroethylene|Teflon]], is known to cause two kinds of cancer.<ref>{{cite web |url= https://www.scientificamerican.com/article/erin-brockovich-blasts-u-s-regulation-of-toxic-chemicals/ |title= Erin Brockovich Blasts U.S. Regulation of Toxic Chemicals |website= scientificamerican.com | publisher= Scientific American |date= 28 December 2020}}</ref><ref>{{cite news |title=Environmental Pollutant, PFOA, Associated with Increased Risk of Kidney Cancer |url=https://dceg.cancer.gov/news-events/news/2020/pfoa-kidney |work=[[National Cancer Institute]] |date=24 September 2020}}</ref>

Chemotherapy drugs such as [[Platinum-based antineoplastic|platinum-based]] compounds are [[carcinogens]] that increase the risk of [[Secondary malignant neoplasm|secondary cancers]]<ref name=cds/>

[[Azathioprine]], an [[immunosuppressive medication]], is a [[carcinogen]] that can cause [[primary tumors]] to develop.<ref name=cds/>

=== Diet and exercise ===
{{Main|Diet and cancer}}
{{anchor|Diet}}Diet, [[Sedentary lifestyle|physical inactivity]], and [[obesity]] are related to up to 30–35% of cancer deaths.<ref name=Enviro2008/><ref name="Nutri06">{{cite journal |vauthors=Kushi LH, Byers T, Doyle C, Bandera EV, McCullough M, McTiernan A, Gansler T, Andrews KS, Thun MJ |s2cid=19823935 |title=American Cancer Society Guidelines on Nutrition and Physical Activity for cancer prevention: reducing the risk of cancer with healthy food choices and physical activity |journal=CA: A Cancer Journal for Clinicians |volume=56 |issue=5 |pages=254–81; quiz 313–14 |year=2006 |pmid=17005596 |doi=10.3322/canjclin.56.5.254|doi-access=free }}</ref> In the United States, excess body weight is associated with the development of many types of cancer and is a factor in 14–20% of cancer deaths.<ref name="Nutri06"/> A UK study including data on over 5 million people showed higher [[body mass index]] to be related to at least 10 types of cancer and responsible for around 12,000 cases each year in that country.<ref name="BhaskaranLancet">{{cite journal |vauthors=Bhaskaran K, Douglas I, Forbes H, dos-Santos-Silva I, Leon DA, Smeeth L |title=Body-mass index and risk of 22 specific cancers: a population-based cohort study of 5·24 million UK adults |journal=Lancet |volume=384 |issue=9945 |pages=755–65 |date=August 2014 |pmid=25129328 |doi=10.1016/S0140-6736(14)60892-8 |pmc=4151483}}</ref> Physical inactivity is believed to contribute to cancer risk, not only through its effect on body weight but also through negative effects on the [[immune system]] and [[endocrine system]].<ref name="Nutri06"/> More than half of the effect from the diet is due to [[overnutrition]] (eating too much), rather than from eating too few vegetables or other healthful foods.{{citation needed|date=March 2024}}

Some specific foods are linked to specific cancers. A high-salt diet is linked to [[gastric cancer]].<ref name=pmid18990005/> [[Aflatoxin B1]], a frequent food contaminant, causes liver cancer.<ref name=pmid18990005/> [[Betel nut]] chewing can cause oral cancer.<ref name="pmid18990005">{{cite journal |vauthors=Park S, Bae J, Nam BH, Yoo KY |title=Aetiology of cancer in Asia |journal=Asian Pacific Journal of Cancer Prevention |volume=9 |issue=3 |pages=371–80 |year=2008 |pmid=18990005 |url=http://www.apocpcontrol.org/page/popup_paper_file_view.php?pno=MzcxIFBhcmsucCZrY29kZT04MjI=&pgubun=i|archive-url=https://web.archive.org/web/20110904052252/http://www.apocpcontrol.org/page/popup_paper_file_view.php?pno=MzcxIFBhcmsucCZrY29kZT04MjI=&pgubun=i |archive-date=4 September 2011}}</ref> National differences in dietary practices may partly explain differences in cancer incidence. For example, [[gastric cancer]] is more common in Japan due to its high-salt diet<ref name="pmid19107449">{{Cite book |vauthors=Brenner H, Rothenbacher D, Arndt V |chapter=Epidemiology of Stomach Cancer |title=Cancer Epidemiology |volume=472 |chapter-url={{google books |plainurl=y |id=5v1JAQAAIAAJ |page=467}}|pages = 467–77 | year = 2009 | pmid = 19107449 | doi = 10.1007/978-1-60327-492-0_23 | isbn = 978-1-60327-491-3 | series = Methods in Molecular Biology |issue=5450 |pmc=2166976 }}</ref> while [[Colorectal cancer|colon cancer]] is more common in the United States. Immigrant cancer profiles mirror those of their new country, often within one generation.<ref name="pmid14278899">{{cite journal |vauthors=Buell P, Dunn JE |title=Cancer Mortality Among Japanese Issei and Nisei of California |journal=Cancer |volume=18 |issue=5 |pages=656–64 |date=May 1965 |pmid=14278899 |doi=10.1002/1097-0142(196505)18:5<656::AID-CNCR2820180515>3.0.CO;2-3|doi-access=free }}</ref>

=== Infection ===
{{Main|Infectious causes of cancer}}
Worldwide, approximately 18% of cancer deaths are related to [[infectious disease]]s.<ref name=Enviro2008/> This proportion ranges from a high of 25% in Africa to less than 10% in the developed world.<ref name=Enviro2008/> Viruses<ref>{{cite journal | vauthors = Moore PS, Chang Y | title = Why do viruses cause cancer? Highlights of the first century of human tumour virology | journal = Nature Reviews. Cancer | volume = 10 | issue = 12 | pages = 878–889 | date = December 2010 | pmid = 21102637 | pmc = 3718018 | doi = 10.1038/nrc2961 | publisher = Springer Science and Business Media LLC }}</ref> are the usual infectious agents that cause cancer but [[bacteria]] and [[parasites]] may also play a role. [[Oncovirus]]es (viruses that can cause human cancer) include:

* [[Human papillomavirus]] ([[cervical cancer]]),
* [[Epstein–Barr virus]] ([[B-cell lymphoproliferative disease]] and [[nasopharyngeal carcinoma]]),
* [[Kaposi's sarcoma herpesvirus]] ([[Kaposi's sarcoma]] and primary effusion lymphomas),
* [[Hepatitis B]] and [[hepatitis C]] viruses ([[hepatocellular carcinoma]])
* [[Human T-cell leukemia virus-1]] (T-cell leukemias).
* [[Merkel cell polyomavirus]] ([[Merkel cell carcinoma]])

Bacterial infection may also increase the risk of cancer, as seen in

* ''[[Helicobacter pylori]]''-induced [[gastric carcinoma]].<ref name="Viral04">{{cite journal |vauthors=Pagano JS, Blaser M, Buendia MA, Damania B, Khalili K, Raab-Traub N, Roizman B |title=Infectious agents and cancer: criteria for a causal relation |journal=Seminars in Cancer Biology |volume=14 |issue=6 |pages=453–71 |date=December 2004 |pmid=15489139 |doi=10.1016/j.semcancer.2004.06.009 }}</ref><ref name="LjubojevicSkerlev2014">{{cite journal |vauthors=Ljubojevic S, Skerlev M |title=HPV-associated diseases |journal=Clinics in Dermatology |volume=32 |issue=2 |pages=227–34 |year=2014 |pmid=24559558 |doi=10.1016/j.clindermatol.2013.08.007}}</ref>
* [[Colibactin]], a [[genotoxin]] associated with ''[[Escherichia coli]]'' infection ([[colorectal cancer]])<ref name=cds/>

Parasitic infections associated with cancer include:

* ''[[Schistosoma haematobium]]'' ([[Bladder cancer|squamous cell carcinoma of the bladder]])
* The [[liver fluke]]s, ''[[Opisthorchis viverrini]]'' and ''[[Clonorchis sinensis]]'' ([[cholangiocarcinoma]]).<ref name="pmid20539059">{{cite journal |vauthors=Samaras V, Rafailidis PI, Mourtzoukou EG, Peppas G, Falagas ME |title=Chronic bacterial and parasitic infections and cancer: a review |journal=Journal of Infection in Developing Countries |volume=4 |issue=5 |pages=267–81 |date=June 2010 |pmid=20539059 |doi=10.3855/jidc.819 |url=http://www.jidc.org/index.php/journal/article/download/20539059/387|url-status=live |archive-url=https://web.archive.org/web/20111004123357/http://www.jidc.org/index.php/journal/article/download/20539059/387 |archive-date=4 October 2011|doi-access=free }}</ref>

=== Radiation ===
{{Main|Radiation-induced cancer}}
Radiation exposure such as [[ultraviolet radiation]] and radioactive material is a risk factor for cancer.<ref name=NCI2019Rad>{{cite web |title=Radiation |url=https://www.cancer.gov/about-cancer/causes-prevention/risk/radiation |publisher=National Cancer Institute |access-date=8 June 2019 |language=en |date=29 April 2015}}</ref><ref name=WHO2019>{{cite web |title=Sunlight |url=https://www.cancer.gov/about-cancer/causes-prevention/risk/sunlight |publisher=National Cancer Institute |access-date=8 June 2019 |language=en |date=29 April 2015}}</ref><ref>{{cite web |title=Cancer prevention |url=https://www.who.int/cancer/prevention/en/ |website=WHO |access-date=8 June 2019}}</ref> Many [[non-melanoma skin cancer]]s are due to ultraviolet radiation, mostly from sunlight.<ref name=WHO2019/> Sources of ionizing radiation include [[medical imaging]] and [[radon]] gas.<ref name=WHO2019/>

Ionizing radiation is not a particularly strong [[mutagen]].<ref name=Little>{{cite book |veditors=Kufe DW, Pollock RE, Weichselbaum RR, Bast RC, Gansler TS, Holland JF, Frei E |title=Cancer medicine | vauthors = Little JB |chapter=Chapter 14: Ionizing Radiation |edition=6th |publisher=B.C. Decker |location=Hamilton, Ont |year=2000 |isbn=978-1-55009-113-7 |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK20793/ |url-status=live |archive-url=https://web.archive.org/web/20160102193148/http://www.ncbi.nlm.nih.gov/books/NBK20793/ |archive-date=2 January 2016}}</ref> Residential exposure to [[radon]] gas, for example, has similar cancer risks as [[passive smoking]]. Radiation is a more potent source of cancer when combined with other cancer-causing agents, such as radon plus tobacco smoke. Radiation can cause cancer in most parts of the body, in all animals and at any age. Children are twice as likely to develop radiation-induced leukemia as adults; radiation exposure before birth has ten times the effect.<ref name=Little/>

Medical use of ionizing radiation is a small but growing source of radiation-induced cancers. Ionizing radiation may be used to treat other cancers, but this may, in some cases, induce a second form of cancer.<ref name=Little/> It is also used in some kinds of [[medical imaging]].<ref name="pmid18046031">{{cite journal |vauthors=Brenner DJ, Hall EJ |s2cid=2760372 |title=Computed tomography—an increasing source of radiation exposure |journal=The New England Journal of Medicine |volume=357 |issue=22 |pages=2277–84 |date=November 2007 |pmid=18046031 |doi=10.1056/NEJMra072149|url=https://repositorio.unal.edu.co/handle/unal/79492 }}</ref>

Prolonged exposure to [[ultraviolet radiation]] from the [[sun]] can lead to [[melanoma]] and other skin malignancies.<ref name=Cleaver>{{cite book |vauthors=Cleaver JE, Mitchell DL |veditors=Bast RC, Kufe DW, Pollock RE |title=Holland-Frei Cancer Medicine |edition=5th |publisher=B.C. Decker |location=Hamilton, Ontario |year=2000 |chapter=15. Ultraviolet Radiation Carcinogenesis |isbn=978-1-55009-113-7 |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK20854/ |access-date=31 January 2011 | display-editors = etal |url-status=live |archive-url=https://web.archive.org/web/20150904102726/http://www.ncbi.nlm.nih.gov/books/NBK20854/ |archive-date=4 September 2015}}</ref> Clear evidence establishes ultraviolet radiation, especially the non-ionizing medium wave [[UVB]], as the cause of most non-melanoma [[skin cancer]]s, which are the most common forms of cancer in the world.<ref name=Cleaver/>

Non-ionizing [[radio frequency]] radiation from mobile phones, [[electric power transmission]] and other similar sources has been described as a [[possible carcinogen]] by the [[World Health Organization]]'s [[International Agency for Research on Cancer]].<ref>{{cite web |title=IARC classifies radiofrequency electromagnetic fields as possibly carcinogenic to humans |url=http://www.iarc.fr/en/media-centre/pr/2011/pdfs/pr208_E.pdf |website=World Health Organization |url-status=live |archive-url=https://web.archive.org/web/20110601063650/http://www.iarc.fr/en/media-centre/pr/2011/pdfs/pr208_E.pdf |archive-date=1 June 2011}}</ref> Evidence, however, has not supported a concern.<ref name=NCI2019EF>{{cite web |title=Electromagnetic Fields and Cancer |url=https://www.cancer.gov/about-cancer/causes-prevention/risk/radiation/electromagnetic-fields-fact-sheet |publisher=National Cancer Institute |access-date=8 June 2019 |language=en |date=7 January 2019}}</ref><ref name=NCI2019Rad/> This includes that studies have not found a consistent link between mobile phone radiation and cancer risk.<ref>{{cite web |url=https://www.cancer.gov/about-cancer/causes-prevention/risk/radiation/cell-phones-fact-sheet |title=Cell Phones and Cancer Risk – National Cancer Institute |publisher=Cancer.gov |date=8 May 2013 |access-date=28 March 2018}}</ref>

=== Heredity ===
{{Main|Cancer syndrome}}
The vast majority of cancers are non-hereditary (sporadic). [[Hereditary cancer]]s are primarily caused by an inherited genetic defect. Less than 0.3% of the population are carriers of a genetic mutation that has a large effect on cancer risk and these cause less than 3–10% of cancer.<ref name=Expert09>{{cite journal |vauthors=Roukos DH |s2cid=24746283 |title=Genome-wide association studies: how predictable is a person's cancer risk? |journal=Expert Review of Anticancer Therapy |volume=9 |issue=4 |pages=389–92 |date=April 2009 |pmid=19374592 |doi=10.1586/era.09.12|doi-access=free }}</ref> Some of these [[syndrome]]s include: certain inherited mutations in the genes ''[[BRCA1]]'' and ''[[BRCA2]]'' with a more than 75% risk of breast cancer and [[ovarian cancer]],<ref name=Expert09/> and [[hereditary nonpolyposis colorectal cancer]] (HNPCC or Lynch syndrome), which is present in about 3% of people with [[colorectal cancer]],<ref name=Lancet10>{{cite journal |vauthors=Cunningham D, Atkin W, Lenz HJ, Lynch HT, Minsky B, Nordlinger B, Starling N |s2cid=25299272 |title=Colorectal cancer |journal=Lancet |volume=375 |issue=9719 |pages=1030–47 |date=March 2010 |pmid=20304247 |doi=10.1016/S0140-6736(10)60353-4}}</ref> among others.

Statistically for cancers causing most mortality, the [[relative risk]] of developing [[colorectal cancer]] when a [[first-degree relative]] (parent, sibling or child) has been diagnosed with it is about 2.<ref name="Kampman2007">{{cite journal | vauthors = Kampman E | title = A first-degree relative with colorectal cancer: what are we missing? | journal = Cancer Epidemiology, Biomarkers & Prevention | volume = 16 | issue = 1 | pages = 1–3 | date = January 2007 | pmid = 17220324 | doi = 10.1158/1055-9965.EPI-06-0984 | doi-access = free }}</ref> The corresponding relative risk is 1.5 for lung cancer,<ref name="CotéLiu2012">{{cite journal | vauthors = Coté ML, Liu M, Bonassi S, Neri M, Schwartz AG, Christiani DC, Spitz MR, Muscat JE, Rennert G, Aben KK, Andrew AS, Bencko V, Bickeböller H, Boffetta P, Brennan P, Brenner H, Duell EJ, Fabianova E, Field JK, Foretova L, Friis S, Harris CC, Holcatova I, Hong YC, Isla D, Janout V, Kiemeney LA, Kiyohara C, Lan Q, Lazarus P, Lissowska J, Le Marchand L, Mates D, Matsuo K, Mayordomo JI, McLaughlin JR, Morgenstern H, Müeller H, Orlow I, Park BJ, Pinchev M, Raji OY, Rennert HS, Rudnai P, Seow A, Stucker I, Szeszenia-Dabrowska N, Dawn Teare M, Tjønnelan A, Ugolini D, van der Heijden HF, Wichmann E, Wiencke JK, Woll PJ, Yang P, Zaridze D, Zhang ZF, Etzel CJ, Hung RJ | title = Increased risk of lung cancer in individuals with a family history of the disease: a pooled analysis from the International Lung Cancer Consortium | journal = European Journal of Cancer | volume = 48 | issue = 13 | pages = 1957–68 | date = September 2012 | pmid = 22436981 | doi = 10.1016/j.ejca.2012.01.038 | pmc = 3445438 }}</ref> and 1.9 for [[prostate cancer]].<ref name="Watkins BrunerMoore2003">{{cite journal | vauthors = Bruner DW, Moore D, Parlanti A, Dorgan J, Engstrom P | title = Relative risk of prostate cancer for men with affected relatives: systematic review and meta-analysis | journal = International Journal of Cancer | volume = 107 | issue = 5 | pages = 797–803 | date = December 2003 | pmid = 14566830 | doi = 10.1002/ijc.11466 | s2cid = 25591527 }}</ref> For breast cancer, the relative risk is 1.8 with a first-degree relative having developed it at 50 years of age or older, and 3.3 when the relative developed it when being younger than 50 years of age.<ref name="Singletary2003">{{cite journal | vauthors = Singletary SE | title = Rating the risk factors for breast cancer | journal = Annals of Surgery | volume = 237 | issue = 4 | pages = 474–482 | date = April 2003 | pmid = 12677142 | pmc = 1514477 | doi = 10.1097/01.SLA.0000059969.64262.87 }}</ref>

Taller people have an increased risk of cancer because they have more cells than shorter people. Since height is genetically determined to a large extent, taller people have a heritable increase in cancer risk.<ref>{{cite journal | vauthors = Green J, Cairns BJ, Casabonne D, Wright FL, Reeves G, Beral V | title = Height and cancer incidence in the Million Women Study: prospective cohort, and meta-analysis of prospective studies of height and total cancer risk | journal = The Lancet. Oncology | volume = 12 | issue = 8 | pages = 785–94 | date = August 2011 | pmid = 21782509 | pmc = 3148429 | doi = 10.1016/S1470-2045(11)70154-1 }}</ref>

=== Physical agents ===
Some substances cause cancer primarily through their physical, rather than chemical, effects.<ref name=Maltoni>{{cite book |vauthors=Maltoni CF, Holland JF |veditors=Bast RC, Kufe DW, Pollock RE |title=Holland-Frei Cancer Medicine |edition=5th |publisher=B.C. Decker |location=Hamilton, Ontario |year=2000 |chapter=Chapter 16: Physical Carcinogens |isbn=978-1-55009-113-7 |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK20770/ |access-date=31 January 2011 | display-editors = etal |url-status=live |archive-url=https://web.archive.org/web/20150904102726/http://www.ncbi.nlm.nih.gov/books/NBK20770/ |archive-date=4 September 2015}}</ref> A prominent example of this is prolonged exposure to [[asbestos]], naturally occurring mineral fibers that are a major cause of [[mesothelioma]] (cancer of the [[serous membrane]]) usually the serous membrane surrounding the lungs.<ref name=Maltoni/> Other substances in this category, including both naturally occurring and synthetic asbestos-like fibers, such as [[wollastonite]], [[attapulgite]], [[glass wool]] and [[rock wool]], are believed to have similar effects.<ref name=Maltoni/> Non-fibrous particulate materials that cause cancer include powdered metallic [[cobalt]] and [[nickel]] and [[crystalline silica]] ([[quartz]], [[cristobalite]] and [[tridymite]]).<ref name=Maltoni/> Usually, physical carcinogens must get inside the body (such as through inhalation) and require years of exposure to produce cancer.<ref name=Maltoni/>

Physical trauma resulting in cancer is relatively rare.<ref name=Gaeta>{{cite book | vauthors = Gaeta JF | veditors = Bast RC, Kufe DW, Pollock RE |title=Holland-Frei Cancer Medicine |edition=5th |publisher=B.C. Decker |location=Hamilton, Ontario |year=2000 |chapter=Chapter 17: Trauma and Inflammation |isbn=978-1-55009-113-7 |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK20784/ |access-date=27 January 2011|display-editors=etal |url-status=live |archive-url=https://web.archive.org/web/20150904102726/http://www.ncbi.nlm.nih.gov/books/NBK20784/ |archive-date=4 September 2015}}</ref> Claims that breaking bones resulted in bone cancer, for example, have not been proven.<ref name=Gaeta/> Similarly, physical trauma is not accepted as a cause for cervical cancer, breast cancer or brain cancer.<ref name=Gaeta/> One accepted source is frequent, long-term application of hot objects to the body. It is possible that repeated burns on the same part of the body, such as those produced by [[kanger]] and kairo heaters (charcoal [[hand warmer]]s), may produce skin cancer, especially if carcinogenic chemicals are also present.<ref name=Gaeta/> Frequent consumption of scalding hot tea may produce esophageal cancer.<ref name=Gaeta/> Generally, it is believed that cancer arises, or a pre-existing cancer is encouraged, during the process of healing, rather than directly by the trauma.<ref name=Gaeta/> However, repeated injuries to the same tissues might promote excessive cell proliferation, which could then increase the odds of a cancerous mutation.{{citation needed|date=March 2024}}

Chronic [[inflammation]] has been hypothesized to directly cause mutation.<ref name=Gaeta/><ref name="ColottaAllavena2009">{{cite journal |vauthors=Colotta F, Allavena P, Sica A, Garlanda C, Mantovani A |title=Cancer-related inflammation, the seventh hallmark of cancer: links to genetic instability |journal=Carcinogenesis |volume=30 |issue=7 |pages=1073–81 |date=July 2009 |pmid=19468060 |doi=10.1093/carcin/bgp127 |type=review|doi-access=free }}</ref> Inflammation can contribute to proliferation, survival, angiogenesis and migration of cancer cells by influencing the [[tumor microenvironment]].<ref>{{cite journal |vauthors=Ungefroren H, Sebens S, Seidl D, Lehnert H, Hass R |title=Interaction of tumor cells with the microenvironment |journal=Cell Communication and Signaling |volume=9 |page=18 |date=September 2011 |pmid=21914164 |doi=10.1186/1478-811X-9-18 |number=18 |pmc=3180438 |doi-access=free }}</ref><ref>{{cite journal |vauthors=Mantovani A |title=Molecular pathways linking inflammation and cancer |journal=Current Molecular Medicine |volume=10 |issue=4 |pages=369–73 |date=June 2010 |pmid=20455855 |doi=10.2174/156652410791316968 |type=review}}</ref> [[Oncogene]]s build up an inflammatory pro-tumorigenic microenvironment.<ref>{{cite journal |vauthors=Borrello MG, Degl'Innocenti D, Pierotti MA |title=Inflammation and cancer: the oncogene-driven connection |journal=Cancer Letters |volume=267 |issue=2 |pages=262–70 |date=August 2008 |pmid=18502035 |doi=10.1016/j.canlet.2008.03.060 |type=review}}</ref>

=== Hormones ===
[[Hormone]]s also play a role in the development of cancer by promoting [[cell growth|cell proliferation]].<ref name=Henderson>{{cite book |vauthors=Henderson BE, Bernstein L, Ross RK |veditors=Bast RC, Kufe DW, Pollock RE |title=Holland-Frei Cancer Medicine |edition=5th |publisher=B.C. Decker |location=Hamilton, Ontario |year=2000 |chapter=Chapter 13: Hormones and the Etiology of Cancer |isbn=978-1-55009-113-7 |chapter-url=https://www.ncbi.nlm.nih.gov/books/NBK20759/ |access-date=27 January 2011 | display-editors = etal |url-status=live |archive-url=https://web.archive.org/web/20170910174411/https://www.ncbi.nlm.nih.gov/books/NBK20759/ |archive-date=10 September 2017}}</ref> [[Insulin-like growth factor]]s and their binding proteins play a key role in cancer cell proliferation, differentiation and [[apoptosis]], suggesting possible involvement in carcinogenesis.<ref>{{cite journal |vauthors=Rowlands MA, Gunnell D, Harris R, Vatten LJ, Holly JM, Martin RM |title=Circulating insulin-like growth factor peptides and prostate cancer risk: a systematic review and meta-analysis |journal=International Journal of Cancer |volume=124 |issue=10 |pages=2416–29 |date=May 2009 |pmid=19142965 |pmc=2743036 |doi=10.1002/ijc.24202}}</ref>

Hormones are important agents in sex-related cancers, such as cancer of the breast, [[endometrium]], prostate, ovary and [[testicle|testis]] and also of [[thyroid cancer]] and [[bone cancer]].<ref name=Henderson/> For example, the daughters of women who have breast cancer have significantly higher levels of [[estrogen]] and [[progesterone]] than the daughters of women without breast cancer. These higher hormone levels may explain their higher risk of breast cancer, even in the absence of a breast-cancer gene.<ref name=Henderson/> Similarly, men of African ancestry have significantly higher levels of [[testosterone]] than men of European ancestry and have a correspondingly higher level of prostate cancer.<ref name=Henderson/> Men of Asian ancestry, with the lowest levels of testosterone-activating [[androstanediol glucuronide]], have the lowest levels of prostate cancer.<ref name=Henderson/>

Other factors are relevant: obese people have higher levels of some hormones associated with cancer and a higher rate of those cancers.<ref name=Henderson/> Women who take [[Hormone replacement therapy (menopause)|hormone replacement therapy]] have a higher risk of developing cancers associated with those hormones.<ref name=Henderson/> On the other hand, people who exercise far more than average have lower levels of these hormones and lower risk of cancer.<ref name=Henderson/> [[Osteosarcoma]] may be promoted by [[growth hormone]]s.<ref name=Henderson/> Some treatments and prevention approaches leverage this cause by artificially reducing hormone levels and thus discouraging hormone-sensitive cancers.<ref name=Henderson/>

=== Autoimmune diseases ===
There is an association between [[celiac disease]] and an increased risk of all cancers. People with untreated celiac disease have a higher risk, but this risk decreases with time after diagnosis and strict treatment. This may be due to the adoption of a [[gluten-free diet]], which seems to have a protective role against the development of malignancy in people with celiac disease. However, the delay in diagnosis and initiation of a gluten-free diet seems to increase the risk of malignancies.<ref name="pmid26402826">{{cite journal |vauthors=Han Y, Chen W, Li P, Ye J |title=Association Between Coeliac Disease and Risk of Any Malignancy and Gastrointestinal Malignancy: A Meta-Analysis |journal=Medicine |volume=94 |issue=38 |pages=e1612 |date=September 2015 |pmid=26402826 |pmc=4635766 |doi=10.1097/MD.0000000000001612}}</ref> Rates of gastrointestinal cancers are increased in people with [[Crohn's disease]] and [[ulcerative colitis]], due to chronic inflammation. [[immunotherapy|Immunomodulators]] and [[biological therapy for inflammatory bowel disease|biologic agents]] used to treat these diseases may promote the development of extra-intestinal malignancies.<ref>{{cite journal |vauthors=Axelrad JE, Lichtiger S, Yajnik V |title=Inflammatory bowel disease and cancer: The role of inflammation, immunosuppression, and cancer treatment |journal=World Journal of Gastroenterology |volume=22 |issue=20 |pages=4794–801 |date=May 2016 |pmid=27239106 |pmc=4873872 |doi=10.3748/wjg.v22.i20.4794 |doi-access=free }}</ref>