The short answer
H. pylori is a common stomach bacterium classified as a human carcinogen. Most infected people never get stomach cancer, but in a trial in China, treating the infection cut stomach cancer by nearly half over 22 years.
In 1994 the WHO's IARC classified H. pylori as a human carcinogen. That reflects strong evidence of a link, not a large risk for any one person.
About two-thirds of the world's population carries H. pylori, and in older US survey data (1999-2000) about 21 percent of non-Hispanic White adults, 52 percent of non-Hispanic Black adults and 64 percent of Mexican American adults were infected.
Most people with H. pylori never develop stomach cancer; stomach cancer accounts for about 1.5 percent of new United States cancers, an estimated 31,510 cases in 2026 (American Cancer Society projection).
In a trial in China, two weeks of antibiotics cut gastric cancer by nearly 50 percent over 22 years, according to NCI.
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54 sec · Captioned · H. pylori is a stomach cancer risk you can test for and treat with antibiotics.
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This page covers H. pylori and stomach cancer: how big the risk is, what the trials show, and who is tested.
A common infection with an uncommon consequence
Helicobacter pylori is a bacterium that lives in the stomach lining. About two-thirds of the world carries it. In the United States, how common it is depends on background. NCI cites older survey data (1999-2000). It found about 21 percent of non-Hispanic White adults, 52 percent of non-Hispanic Black adults and 64 percent of Mexican American adults were infected.
In 1994 the World Health Organization's IARC classified H. pylori as a human carcinogen. That says the evidence of a link is strong. It does not say the risk to any one person is large.
Stomach cancer makes up about 1.5 percent of new cancers in the United States. The American Cancer Society projects about 31,510 new cases and 10,740 deaths in 2026, as published in SEER Stat Facts. Compare that with two-thirds of the world carrying the bacterium. Most people who carry it never get stomach cancer.
Why treatment is worth discussing
A trial in China gave people two weeks of antibiotics. NCI reports that it cut stomach cancer by nearly 50 percent over 22 years. Another trial found that people treated for the infection were half as likely to develop additional gastric cancer lesions than those given placebo.
In a Chinese trial of first-degree relatives of people with stomach cancer, NCI reports stomach cancer fell from 2.7 percent with placebo to 1.2 percent with treatment.
H. pylori is also tied to gastric MALT lymphoma. NCI says that after standard antibiotics, about half of patients show resolution of the lymphoma by 3 months. Others may resolve after 12 to 18 months of watching.
Who is tested
NCI says people with an active stomach or duodenal ulcer, or a documented history of ulcers, should be tested. Most experts agree there is not enough evidence to test and treat everyone. Ask your care team whether your history, family history or symptoms call for testing.
How testing works
MedlinePlus describes four kinds of tests. A breath test uses a special urea pill. A stool test looks for the bacteria. An endoscopy lets a doctor take a biopsy. A blood test looks for antibodies, but it cannot show whether the infection is current or past.
You may need to stop certain medicines for two weeks to a month before testing. Ask how to prepare. Do not change any medicine on your own.
After treatment
MedlinePlus says follow-up testing may be needed to confirm the infection is gone, because the bacteria can regrow if any remain. Ask when yours is planned. Which antibiotics suit you is a decision for your care team.
NCI describes intestinal metaplasia and atrophic gastritis as precancerous changes. If an endoscopy showed either one, ask your care team about follow-up.
Ongoing indigestion, trouble swallowing, vomiting, unplanned weight loss, or black stools need prompt review. Call your care team right away. That holds whatever your test results say. Vomiting blood or severe belly pain is an emergency: call 911.
Sources
Common questions
I have H. pylori. What is my actual chance of getting stomach cancer?
For most people in the United States it is low. Stomach cancer makes up about 1.5 percent of new cancers nationally, and most of the two-thirds of the world carrying H. pylori never develop it. Your own risk depends on things like family history, bacterial strain, diet and smoking. Ask your care team about your situation.
Which test should I ask about?
MedlinePlus lists four kinds: a urea breath test, a stool test, a biopsy during an upper endoscopy, and a blood test. A blood test cannot tell a current infection from a past one. You may need to stop certain medicines for two weeks to a month before testing. Ask your care team how to prepare, and do not stop any medicine on your own.
Does treatment work, and how would I know?
A trial in China found two weeks of antibiotics cut stomach cancer by nearly 50 percent over 22 years. MedlinePlus says follow-up testing may be needed to confirm the infection is gone, since bacteria can regrow if any remain. Ask whether a follow-up test is planned.
Should my family be tested too?
A trial in China gave treatment to first-degree relatives of people with stomach cancer. Stomach cancer fell from 2.7 percent with placebo to 1.2 percent with treatment, according to NCI. Whether testing makes sense for your family is a question for your care team.
If I clear the infection, is my risk gone?
NCI describes intestinal metaplasia and atrophic gastritis as precancerous changes that develop over many years. Ask your care team whether treatment lowers your own risk and whether you need follow-up.
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Written by: Cancer ExplainedSources last checked: 2026-08-13 what this meansLast updated: 2026-10-02Next planned review: 2027-07-30
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Cancer Explained does not originate medical claims. Every page restates guidance already published by the National Cancer Institute, the CDC, the USPSTF and the FDA, in plain language, with the source cited so you can check the original yourself. AI does the translating and organizing; automated checks test claims, citations, clarity and safety before anything publishes, and this is translation and navigation, not clinical judgment. Nothing here is personal medical advice, and no page can account for your particular situation.
Editorial status: Source checked — This page was written with AI assistance and then compared with the sources listed on it, looking for statements those sources do not back up. That check is not a sentence-by-sentence record and can miss errors. It is not a medical review, and it does not confirm the page is complete or right for your situation.
Human medical review: not completed. Pages here are not signed off by a clinician before they publish. That is not an oversight we are quietly working around: we restate published guidance and cite it, so the authority belongs to the source rather than to us, and every page names where its claims come from — you can verify us instead of trusting us. Where a volunteer clinician has reviewed a page, their name and credentials appear on it; where no name appears, no clinician has checked it. We are glad to have reviewers and are recruiting them, and we do not hold pages back waiting for one. Use this site to understand your situation and to ask better questions of the people treating you.
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