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, the vast majority of people who carry this germ in their stomachs never develop cancer.

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, and 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 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 intrinsic factor (IF), which is a substance needed to absorb vitamin B12 from foods. 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, the exact increase in the risk of stomach cancer is not known.

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

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

Hereditary diffuse gastric cancer is an inherited condition 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%. Researchers recently discovered the gene (E-cadherin/CDH1) responsible for this condition, and genetic testing is available at some cancer centers.

Hereditary non-polyposis colorectal cancer (HNPCC, also known as Lynch syndrome) and familial adenomatous polyposis (FAP) are also inherited genetic disorders. They cause a greatly increased risk of getting colorectal cancer and a slightly increased risk of getting stomach cancer in family members who have these gene mutations.

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

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 ("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 clear what role the virus plays in the development of stomach cancer.

Certain occupations

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

Last Medical Review: 11/07/2008
Last Revised: 11/07/2008