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Stomach cancer often develops slowly, sometimes after long-term changes in the stomach lining. While there is no single known cause, certain infections, lifestyle habits, and genetic changes can increase your risk.

What causes stomach cancer?

Stomach cancer doesn’t have a single known cause, but several factors can raise or lower your risk. Often it's not clear exactly how these factors might affect how cells in the stomach become cancer cells.

Risk factors for stomach cancer include:

• Age, sex, race/ethnicity, and geography
• Body weight, diet, tobacco and alcohol use, and other lifestyle factors
• Family history and inherited conditions
• Past medical history, including certain infections and other conditions
• Certain occupations

Precancerous changes in the stomach

Some types of changes in the inner lining of the stomach might lead to stomach cancer.

Atrophic gastritis: In this condition, there are fewer gland cells in the stomach lining than normal. There is also inflammation, in which the stomach cells are damaged by cells of the immune system.

Atrophic gastritis often is caused by infection with H pylori bacteria (see Risk Factors for Stomach Cancer). It can also be caused by a reaction known as autoimmune gastritis, in which a person’s immune system attacks the cells lining the stomach.

Some people with this condition go on to develop other stomach problems, including pernicious anemia, intestinal metaplasia, dysplasia, and stomach cancer.

Intestinal metaplasia: In this condition, the cells that normally line the inside of the stomach are replaced by cells that look like the cells that usually line the intestine. People with this condition often have chronic atrophic gastritis as well. This can also be related to H pylori infection.

Dysplasia: Both atrophic gastritis and intestinal metaplasia can lead to having too few gland cells in the stomach, which would normally secrete substances that help protect the cells in the inner lining. Damage to the DNA (genes) inside these cells can sometimes lead to dysplasia, in which the cells become larger and look very abnormal, more like cancer cells. In some cases, dysplasia can then progress to stomach cancer.

Changes in genes (DNA) in stomach cancer cells

It’s not always clear why these changes develop in stomach cells, but researchers have learned how some stomach cancers form. For instance:

• H pylori bacteria, particularly certain subtypes, can convert substances in some foods into chemicals that cause DNA changes in the cells lining the stomach. This may help explain why certain foods such as preserved meats increase a person’s risk for stomach cancer.
• On the other hand, some foods that might lower stomach cancer risk, such as fruits and vegetables, contain antioxidants (like vitamins A and C) that can block substances that damage a cell’s DNA.

How gene changes (mutations) can lead to cancer

Genes are pieces of DNA inside each cell that carry instructions for how the cell works. Certain genes help control when our cells grow, divide to make new cells, or repair mistakes in DNA. They also cause cells to die when they’re supposed to. If these genes aren’t working properly, it can lead to cells growing out of control.

Cancer develops when changes (mutations) in certain genes lead to abnormal cell growth. To learn more, see Genes and Cancer.

Inherited versus acquired gene mutations

Some people inherit a gene mutation from a parent that increases their stomach cancer risk. But inherited mutations are thought to cause only a small percentage of stomach cancers.

Most of the gene changes that lead to stomach cancer happen during a person’s lifetime. Some of these acquired mutations might be caused by risk factors such as H pylori infection or tobacco use. But some gene changes may just be random events that sometimes happen inside cells, without having an outside cause.

Can stomach cancer be prevented?

There is no sure way to prevent stomach cancer, but there are things you can do to help lower your risk.

Diet, nutrition, body weight, physical activity, and alcohol use

Having excess body weight (overweight or obesity) increases the risk of some types of stomach cancer, so getting to and staying at a healthy weight might lower your risk.

Getting regular physical activity might also help lower your risk of stomach cancer.

Aside from possible effects on stomach cancer risk, staying at a healthy weight and being active may also lower your risk of several other cancers and health problems.

A diet that includes plenty of fresh fruits and vegetables probably also lowers stomach cancer risk. Citrus fruits (such as oranges, lemons, and grapefruit) may be especially helpful, but be aware that grapefruit and grapefruit juice can change the blood levels of certain drugs you take. Talk to your health care team about this before adding grapefruit to your diet.

The American Cancer Society recommends that you follow a healthy eating pattern, which includes a variety of colorful fruits and vegetables and whole grains, and avoids or limits red and processed meats, sugar-sweetened beverages, and highly processed foods.

Drinking alcohol probably increases the risk of stomach cancer, so avoiding or limiting alcohol might lower your risk.

For more on diet, body weight, physical activity, and alcohol use, see the ?American Cancer Society Guideline for Diet and Physical Activity for Cancer Prevention.

Studies that have looked at other dietary factors, such as taking dietary supplements or drinking tea (particularly green tea) have not led to firm conclusions when it comes to lowering stomach cancer risk. Further research is needed in these areas.

Not smoking

Smoking can increase the risk of cancers of the upper stomach (the portion closest to the esophagus). Tobacco use increases the risk for many other types of cancer as well. If you don’t use tobacco, don’t start. If you already do and want help quitting, call the American Cancer Society at 1-800-227-2345.

Treating H pylori infection

It's not yet clear if people whose stomach linings are chronically infected with the H pylori bacteria but who do not have any symptoms should be treated with antibiotics. Some studies have suggested that giving antibiotics to people with H pylori infection might lower the number of precancerous lesions in the stomach and reduce the risk of developing stomach cancer. But not all studies have found this.

While it’s not yet clear if all people with H pylori infection should be treated, some research has shown that it might be helpful to test for H pylori and treat people who are at higher risk for stomach cancer, such as those with atrophic gastritis, intestinal metaplasia, or a family history of stomach cancer. Doctors also often recommend that household contacts of people who are known to have H pylori be tested for infection and treated, if needed.

If your doctor thinks you might have H pylori infection, there are several ways to test for this, including a breath test, a blood test, a stool test, and an endoscopy procedure, in which a biopsy is done. (See Tests for Stomach Cancer.)

Aspirin use

Regular use of aspirin or other non-steroidal anti-inflammatory drugs (NSAIDs) such as ibuprofen or naproxen seems to lower the risk of stomach cancer. These medicines can also lower the risk of developing colon polyps and colon cancer. But they can also cause serious, and even life-threatening, internal bleeding and other potential health risks in some people, so talk with your doctor before taking any of these drugs regularly.

Most doctors consider any reduced cancer risk an added benefit for people who take these drugs for other reasons, such as to treat arthritis. But doctors do not routinely recommend taking NSAIDs specifically to prevent stomach or other cancers.

For people with inherited syndromes that increase stomach cancer risk