Helicobacter pylori and Stomach Cancer: What the New Study Shows

In short: According to a new IARC analysis published in The Lancet Oncology, infections were linked to about 12% of all new cancer cases in 2024 (around 2.3 million). The largest share, roughly 760,000, is attributed to the bacterium Helicobacter pylori. Most infected people never develop cancer, but the infection can be detected with a test and discussed with a doctor early.

Author: Ondřej Dvořák

In this article

Helicobacter pylori and cancer: what the study found
Why Helicobacter pylori comes first
What “linked to infection” means
When to talk to your doctor
Which tests for Helicobacter pylori exist
What to do: three steps
Frequently asked questions

Helicobacter pylori and cancer: what the study found

The analysis was published in late September 2026 in The Lancet Oncology and is based on estimates from the International Agency for Research on Cancer (IARC), part of the WHO. The authors examined 12 infectious agents known to be able to cause cancer. In 2024, infections were linked to an estimated 2.3 million new cancer cases, roughly one in eight. Five agents account for almost all of them:

Agent	Estimated cases in 2024	Typically associated cancers
Helicobacter pylori	760,000	stomach cancer
HPV (human papillomavirus)	750,000	cervical cancer and other cancers of the genital area, anus and throat
Hepatitis B virus	360,000	liver cancer
Epstein-Barr virus	260,000	nasopharyngeal cancers, lymphomas, some stomach cancers
Hepatitis C virus	160,000	liver cancer

Source: IARC press release No. 387, study in The Lancet Oncology. Figures are rounded estimates.

Why Helicobacter pylori comes first

The reason is simple: it is an extremely common infection. Estimates suggest that around half of the world’s population is infected, and in most people it causes no symptoms at all. Only some strains of the bacterium cause stomach ulcers, and in some infected people, years of chronic inflammation of the stomach lining can eventually lead to stomach cancer.

The geographic distribution is also notable. East Asia accounts for 42% of all infection-related cases, mainly because of H. pylori and the hepatitis B virus. More than three quarters of cases occur in low- and middle-income countries. The study authors point out inequalities: these countries carry a disproportionately large burden.

What “linked to infection” means

The estimate of “cases attributable to infection” tells you how many cancers probably would not have developed if the infection did not exist. It does not say that every infected person will fall ill. One of the experts commenting on the study stressed that the vast majority of people with H. pylori, HPV or hepatitis never develop cancer. The reverse is also true: most cancers are not caused by infections.

Keep perspective: The practical takeaway of the study is not fear. Unlike many other risks, infectious causes of cancer can be identified and dealt with: either by avoiding the infection or by treating it before a tumor develops.

When to talk to your doctor

A report about numbers should not send anyone for tests without a reason. A conversation with your doctor does make sense if:

you have long-lasting or recurring stomach problems that do not go away,
you have had a stomach or duodenal ulcer,
stomach cancer has occurred in someone in your close family,
you notice unexplained weight loss, repeated vomiting, difficulty swallowing or black stools. In that case, do not wait and see a doctor as soon as possible.

How the infection usually starts and shows itself is covered in How Do You Know If You Have Helicobacter Pylori?, so we do not repeat it here.

Which tests for Helicobacter pylori exist

There are several tests and they differ in what they show. Detailed guidance is in our H. pylori test at home guide. Here are just the essentials:

Test	What it detects	What to watch out for
Breath test (urea breath test)	presence of an active infection	done at a doctor’s office or lab; a pause in certain medications is needed beforehand
Stool antigen test	presence of an active infection	also available as a home test; the same restrictions apply as for the breath test
Blood antibodies	past or current contact with the bacterium	may stay positive even after the infection has cleared, so it is not suitable for checking the result of treatment
Gastroscopy with a biopsy	the infection and the condition of the stomach lining	performed by a doctor, typically for symptoms or warning signs

Before a breath test or a stool test, stomach medications (proton pump inhibitors) and antibiotics can affect the result. Do not stop anything on your own, though: your doctor decides how long the pause should be.

What to do: three steps

Find out whether you have the infection. Stool and blood tests are available. A home test is indicative only.
If the result is positive, see a doctor. Treatment is decided by your doctor, usually a combination of prescription medicines including antibiotics. Do not start them on your own.
Check that the treatment worked. Your doctor will usually recommend a follow-up test after treatment ends, so it is clear that the infection has gone.

Where to start: The simplest first step is to find out where you stand. You can do tests for Helicobacter pylori at home and then discuss the result with your doctor. A test does not replace an examination or treatment by a doctor.

Frequently asked questions

Question	Answer
Does Helicobacter pylori cause stomach cancer?	According to the new IARC analysis, H. pylori infection is the largest single infectious cause of cancer worldwide and is linked mainly to stomach cancer. This does not mean that every infected person will get cancer: most people with the infection never develop a tumor.
How many people with H. pylori develop stomach cancer?	We do not give an exact percentage here because we would have to base it on a specific study. The experts consulted do stress, however, that the vast majority of infected people do not develop cancer. The risk depends, among other things, on the characteristics of the bacterial strain, individual factors and family history.
Should I get tested even if I have no symptoms?	The infection often causes no symptoms. A test makes the most sense if you have long-lasting stomach problems, a history of stomach ulcers or stomach cancer in your family. Talk to your doctor about testing when you have no symptoms.
Does treating the infection reduce the risk of cancer?	The authors of the analysis and the experts consulted state that the infection can be treated before a tumor develops, and count this among the main routes of prevention. Treatment of the infection, however, is always decided by a doctor.
Which test for Helicobacter pylori is the best?	An active infection is usually detected by a breath test or a stool test, while blood antibodies only show contact with the bacterium. Discuss with your doctor which test to choose. Home tests are indicative only.
Do I have to stop medication before the test?	Stomach medications (proton pump inhibitors) and antibiotics can affect the result of both the breath test and the stool test. Do not stop anything on your own, though: your doctor decides how long the pause should be.
Do the infection and the cancer risk affect children too?	Testing and treatment of children are always decided by a pediatrician. If a child tests positive, contact the pediatrician.
Is a home test for Helicobacter pylori reliable?	A home test is an indicative check that shows whether the infection is probably present. Always discuss a positive result with a doctor, who will decide on the next steps.
Does the study also cover HPV?	Yes, with around 750,000 cases HPV comes a close second. Prevention is vaccination and screening, which is a matter for your doctor.