What Causes Stomach Cancer?
We do not know what causes cancer. Risk factors may increases the chances of developing cancer. It is important to remember that having a risk factor does not guarantee that you will develop cancer, it simply increases your risk. Some factors are under our control (e.g. diet), but we cannot control all factors (e.g. genetics). Scientists are constantly discovering new risk factors. Both discovered and not yet discovered risk factors interact to cause stomach cancer.
The following risk factors have been shown to increase the chance of stomach cancer specifically:
Image credit: Cancer Council NSW
Infection with Helicobacter Pylori (H. Pylori)
H. Pylori infection is a significant risk factor for stomach cancer. H. pylori is a bacteria that is commonly found in the stomach. Many people are infected with H. pylori but few people actually develop stomach cancer. H. pylori may lead to the development of gastritis (inflammation in the stomach wall) and peptic ulcer disease (stomach ulcers) which are sores found in the stomach. Stomach ulcers and inflammation caused by H. Pylori leads to changes in the cells that line the stomach and these changes can lead to cancer.
diet
high consumption of red, smoked, cured or processed meat
high salt intake
high nitrate diet
diet low in vitamin A and C
consuming more than 3 alcoholic beverages per day
lack of refrigerated food
poor-quality drinking water
High Body Mass Index (BMI) and Obesity
It is unclear why an increased BMI is a cancer risk factor. However being overweight or obese can increase the risk of many cancers including stomach cancer.
Type A blood.
It is unclear how why having blood type A is a risk factor for developing stomach cancer.
Occupational Exposure
People who work in the rubber or coal industry have an increased risk of getting stomach cancer due to chronic exposure to cancer causing chemicals.
Cigarette Smoke
Both first-hand and second-hand smoke can increase the risk of developing stomach cancer. The risk increases with the number of cigarettes and the duration of smoking. Quitting smoking decreases the risk of cancer.
Previous Exposure to Radiation
High doses of ionizing radiation can increase the risk of stomach cancer. Ionizing radiation at high doses occurs from exposure to nuclear disasters (e.g. Hiroshima, Fukushima, Cernobyl), treatment with radioisotopes (e.g. treating thyroid cancer) or external beam radiation (e.g. radiation treatment for a previous cancer).
Previous Stomach Surgery
People who have had stomach surgery such as a partial gastrectomy to remove a peptic ulcer are at an increased risk of stomach cancer.
Family History
Sometimes families have a strong pattern of stomach cancer but no specific gene can be identified. Having a first degree relative with stomach cancer increases the likelihood that you may get stomach cancer.
Genetic Factors
Several genetic conditions may cause stomach cancer. If you were diagnosed with stomach cancer at a young age or have a strong family history of stomach cancer, speak to your doctor about getting genetic testing. For more information on genetics and stomach cancer please refer to the lecture from our guest speaker HERE. The following genetic conditions are associated with stomach cancer:
Hereditary diffuse gastric cancer (HDGC): This condition is strongly linked to diffuse type of gastric cancer. Diffuse type of stomach cancer means that the cancer cells are found all over the stomach, rather than in a single tumor, as in the case of intestinal type of stomach cancner. Diffuse type of stomach cancer typically develops in patients who are younger than 40 years old. HDGC is caused by a CDH1 mutation (also known as E-Cadherin gene mutation).
Lynch syndrome (also known as Hereditary Non-polyposis colon cancer): Lynch syndrome is a significant risk factor for colorectal cancer, however it can increase the chances of other cancer such as stomach, endometrial, breast, ovarian, small bowel, prostate, pancreatic, urinary tract, liver, kidney, and bile duct cancers. Lynch syndrome is caused by a mutation in mismatch repair genes that normally function to correct mistakes made in copying DNA.
Familial Adenomatous polyposis (FAP): People with FAP develop multiple polyps in their colon. This condition is a risk factor for colon, stomach and cancer of small intestine. It is caused by a mutation in the APC gene
BRCA-gene mutation: a mutation in BRCA can increase the risk of breast, ovarian, stomach cancer and many other cancer types
Peutz-Jeghers syndrome: is another genetic condition that causes gastrointestinal polyps which can lead to stomach cancer.
Li-Fraumeni syndrome: a rare genetic condition that is a risk factor mainly in breast cancer but also stomach cancer, sarcomas (bone cancer), brain cancer, leukemia, lymphoma and others.
Stomach Conditions
Chronic atrophic gastritis: This condition refers to long term inflammation in the stomach which can increase the chance of developing stomach cancer. Inflammation may be caused by H. pylori infection or may be autoimmune (the body attacks itself leading to inflammation in the stomach)
Intestinal metaplasia: metaplasia is when normal cells in the stomach are replaced by other cells that are normally found in the intestines. These intestinal cells are still normal in the body but are now found in an abnormal location (the stomach) and can be a risk for developing stomach cancer. This abnormal switch in location may be triggered by diet, H. pylori or other factors.
Gastric epithelial dysplasia: dysplasia means that the normal cells of the stomach undergo abnormal changes which causes dysplasia which is a precancerous condition that can develop into adenocarcinoma of the stomach (type of stomach cancer)
Adenomatous gastric polyps: Abnormal polyps may form on the lining of the stomach. These precancerous polyps may turn into stomach cancer.
Pernicious anemia: Vitamin B12 is needed by the body to make red blood cells, which are important in delivering oxygen to the body. In prenicious anemia, the gastrointestinal tract cannot absorb B12, leading to anemia (low red blood cells). People with pernicious anemia may develop polyps in the stomach.
Ménétrier disease: a rare condition where the stomach lining forms too many folds which may lead to stomach cancer.