A risk factor is anything that affects your chance of getting a disease such as cancer. Different cancers have different risk factors. For example, exposing skin to strong sunlight is a risk factor for skin cancer. Smoking is a risk factor for a number of cancers.

But risk factors don't tell us everything. Having a risk factor, or even several risk factors, does not mean that you will get the disease. And many people who get the disease may not have had any known risk factors.

Scientists have found several risk factors that make a person more likely to get stomach cancer. Some of these can be controlled, but others cannot.

Helicobacter pylori infection

Infection with Helicobacter pylori (H pylori) bacteria seems to be a major cause of stomach cancer, especially cancers in the lower (distal) part of the stomach. Long-term infection of the stomach with this germ may lead to inflammation (chronic atrophic gastritis) and pre-cancerous changes of the inner lining of the stomach. Patients with stomach cancer have a higher rate of infection than people without this cancer. H pylori infection is also linked to some types of lymphoma of the stomach. Even so, most people who carry this germ in their stomachs never develop cancer.

Stomach lymphoma

People who have been treated for a certain type of lymphoma of the stomach known as mucosa-associated lymphoid tissue (MALT) lymphoma have an increased risk of getting carcinoma of the stomach. That is probably because MALT lymphoma of the stomach is caused by infection with H pylori bacteria.

Gender

Stomach cancer is more common in men than in women.

Aging

There is a sharp increase in stomach cancer after the age of 50. Most people diagnosed with stomach cancer are in their late 60s, 70s, or 80s.

Ethnicity

In the United States, stomach cancer is more common in Hispanic Americans and African Americans than in non-Hispanic whites. It is most common in Asian/Pacific Islanders.

Geography

Where you live may be important. Stomach cancer is more common in Japan, China, Southern and Eastern Europe, and South and Central America. This disease is less common in Northern and Western Africa, South Central Asia, and North America.

Diet

An increased risk of stomach cancer is seen with diets containing large amounts of smoked foods, salted fish and meat, and pickled vegetables. Nitrates and nitrites are substances commonly found in cured meats. They can be converted by certain bacteria, such as H pylori, into compounds that have been found to cause stomach cancer in animals.

On the other hand, eating fresh fruits and vegetables that contain antioxidant vitamins (such as A and C) appears to lower the risk of stomach cancer.

Tobacco use

Smoking increases stomach cancer risk, particularly for cancers of the upper portion of the stomach closest to the esophagus. The rate of stomach cancer is about doubled in smokers.

Obesity

Being very overweight or obese has emerged as a possible cause of cancers of the cardia (the upper part of the stomach nearest the esophagus), but the strength of this link is not yet clear.

Previous stomach surgery

Stomach cancers are more likely to develop in people who have had part of their stomach removed to treat non-cancerous diseases such as ulcers. This may be because it allows more nitrite-producing bacteria to be present. Also, acid production goes down after ulcer surgery, and there may be reflux (backup) of bile from the small intestine into the stomach. The risk continues to increase for as long as 15 to 20 years after surgery.

Pernicious anemia

Certain cells in the stomach lining normally make a substance needed to absorb vitamin B12 from foods called intrinsic factor (IF). People without enough IF may end up with a vitamin B12 deficiency, which affects the body's ability to make new red blood cells. This condition is called pernicious anemia. Along with anemia (low red blood cell counts), there is an increased risk of stomach cancer for patients with this disease.

Menetrier disease (hypertrophic gastropathy)

This is a condition in which excess growth of the stomach lining leads to the formation of large folds in the lining and to low levels of stomach acid. Because this disease is very rare, it is not known exactly how much this increases the risk of stomach cancer.

Type A blood

Blood type groups refer to certain substances that are normally present on the surface of red blood cells and some other types of cells. These groups are important in matching blood for transfusions. For unknown reasons, people with type A blood have a higher risk of getting stomach cancer.

Inherited cancer syndromes

Some inherited conditions may raise a person's risk of stomach cancer.

Hereditary diffuse gastric cancer: This is an inherited syndrome that greatly increases the risk of developing stomach cancer. This condition is quite rare, but the lifetime stomach cancer risk among affected people is about 70% to 80%. Women with this syndrome also have an increased risk of getting a certain type of breast cancer. This condition is caused by mutations (defects) in the gene (E-cadherin/CDH1). Some cancer centers can test for these genetic mutations.

Hereditary non-polyposis colorectal cancer: HNPCC, also known as Lynch syndrome is an inherited genetic disorder that causes an increased risk of colon cancer. People with this syndrome have an increased risk of getting stomach cancer as well. In most cases, this disorder is caused by a defect in either the gene MLH1 or the gene MSH2, but at least 5 other genes can cause HNPCC: MLH3, MSH6, TGBR2, PMS1, and PMS2.

Familial adenomatous polyposis: FAP is a syndrome where patients get many polyps in the colon as well as in the stomach and intestines. People with this syndrome are at greatly increased risk of getting colorectal cancer and have slightly increased risk of getting stomach cancer. It is caused by mutations in the gene APC.

BRCA1 and BRCA2: People who carry mutations of the inherited breast cancer genes BRCA1 and BRCA2 may also have a higher rate of stomach cancer.

A family history of stomach cancer

People with several first-degree relatives who have had stomach cancer are more likely to develop this disease.

Some types of stomach polyps

Polyps are non-cancerous growths on the lining of the stomach. Most types of polyps (such as hyperplastic polyps or inflammatory polyps) do not appear to increase a person's risk of stomach cancer, but adenomatous polyps -- also called adenomas -- can sometimes develop into cancer.

Epstein-Barr virus infection

This virus causes infectious mononucleosis (also called mono). Almost all adults have been infected with this virus at some time in their lives, usually as children or adolescents. It has been linked to some forms of lymphoma. Epstein-Barr virus has also been found in the stomach cancers of about 5% to 10% of people with this disease. These people tend to have a slower growing, less aggressive cancer with a lower tendency to spread. It isn't yet clear if this virus actually causes stomach cancer, but the virus has been found in stomach cancer cells.

Certain occupations

Workers in the coal, metal, and rubber industries seem to have a higher risk of getting stomach cancer.

Last Medical Review: 11/03/2009
Last Revised: 11/03/2009