Stomach cancer no relation carcinogenesis
Breast 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.  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.  The major estrogen in humans, estradiol, can be metabolized to quinone derivatives that form adducts with DNA.  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.Stomach 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).  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 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 high in fresh fruit and vegetables may reduce the risk. The risk also increases with age.
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