Editing Carcinogen (section)

===Stomach cancer===
[[Stomach cancer]] is the fourth most common cancer [990,000 cases (7.8%), 738,000 deaths (9.7%)].<ref name=Ferlay />  ''[[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).<ref>{{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 }}</ref><ref>{{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 }}</ref>  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.<ref>{{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 }}</ref>