Oxidative stress
Oxidative stress is likely to be involved in age-related development of cancer. The reactive species produced in oxidative stress can cause direct damage to the DNA and are therefore mutagenic, and it may also suppress apoptosis and promote proliferation, invasiveness and metastasis. Infection by "Helicobacter pylori" which increases the production of reactive oxygen and nitrogen species in human stomach is also thought to be important in the development of gastric cancer.