The Gut Bacterium Behind 760,000 Cancers a Year, and 4 Other Culprits

If your gut-health research has ever brought you face to face with Helicobacter pylori (H. pylori), the stomach-dwelling bacterium best known for causing ulcers, you already know that a chronic infection can leave marks on the body long after symptoms fade. A new global analysis puts a hard number on how far that reach extends into cancer: an estimated 2.3 million cancer cases diagnosed worldwide in 2024, roughly 1 in 8 of all cancers that year, are attributable to infection. Five agents, led by H. pylori, account for nearly all of it. For anyone tracking a gut-linked health worry, this isn't an abstract microbiome curiosity, it's a measurable, and largely preventable, slice of the global cancer burden.

Key takeaways

• An estimated 2.3 million new cancer cases in 2024, about 1 in 8 worldwide, are attributable to infection, per a Lancet Oncology analysis led by the International Agency for Research on Cancer (IARC).
• Just five infections account for nearly all of that burden: H. pylori (760,000 cases), HPV (750,000), hepatitis B (360,000), Epstein-Barr virus (260,000), and hepatitis C (160,000).
• H. pylori, the same bacterium behind most stomach ulcers, is the single largest contributor, driving stomach cancer cases concentrated heavily in Eastern Asia.
• The headline caveat: these are modeled estimates built from registry and infection-prevalence data, not confirmation that any one person's cancer was caused by an infection they carried, and the underlying journal paper is paywalled, this article is based on its published abstract and IARC's own public statement about it.

H. Pylori Tops List of Infection-Linked Cancers

An estimated 2.3 million new cancer cases diagnosed worldwide in 2024, about 12% of all cancers that year, are attributable to infection, according to a new analysis published in The Lancet Oncology by a team led by researcher H. Rumgay at IARC, the World Health Organization's cancer research arm. Five infectious agents account for nearly all of that burden. Helicobacter pylori (H. pylori, a bacterium that colonizes the stomach lining) tops the list at 760,000 cases, narrowly ahead of human papillomavirus (HPV) at 750,000. Hepatitis B virus (HBV) accounts for 360,000 cases, Epstein-Barr virus (EBV, a common herpesvirus) for 260,000, and hepatitis C virus (HCV) for 160,000.

Who Carries the Heaviest Infection-Cancer Burden

Three-quarters of infection-attributable cancers occurred in low- and middle-income countries, and the burden is concentrated in specific regions rather than spread evenly around the globe. Eastern Asia alone accounted for 42% of the worldwide total, driven largely by H. pylori and hepatitis B. The analysis also flags a particularly high burden in Sub-Saharan Africa, driven by HPV and Kaposi sarcoma-associated herpesvirus (KSHV, a virus linked to a rare skin and soft-tissue cancer) and worsened where HIV co-infection is common. For anyone in a household affected by chronic H. pylori infection, unresolved hepatitis B or C, or HPV, the geographic skew is a reminder that downstream cancer risk from these infections tracks closely with access to testing, vaccination and care, not just biology.

How Researchers Modeled the Global Cancer Burden

This is a burden-of-disease modeling study, the same broad approach used in long-running global cancer statistics projects, rather than a clinical trial following individual patients over time. Researchers combined cancer-registry incidence data with data on how common each infection is within a population to estimate what share of cancers in each region and cancer type can be statistically attributed to it. That makes it a large-scale, descriptive epidemiological exercise built on established methodology, not an experiment that manipulated any variable directly.

What This Means If You've Had These Infections

None of this means a past or current infection guarantees cancer, and this article isn't a substitute for a conversation with your own doctor. What it does mean is that the underlying risk is well established enough that global health agencies now treat several of these infections as cancer-prevention targets, not just infectious-disease concerns. If you have a history of H. pylori infection, unresolved hepatitis B or C, or fall into an age group eligible for HPV vaccination, this is worth raising directly with a doctor rather than shelving as old news. A systematic review published on the NIH's PubMed Central archive has linked H. pylori eradication therapy to reduced stomach cancer incidence in at-risk populations, though benefit varies by region and by how early treatment happens.

What the Analysis Doesn't Establish

These are population-level estimates, not case-by-case proof. They're built by combining registry data with infection-prevalence estimates, so data quality varies by country, and the method cannot say that a specific person's tumor was caused by the infection they happened to carry. It's also worth being direct about what this article itself rests on: The Lancet Oncology paper sits behind a journal paywall, so this piece is based on the study's published abstract and the public statement IARC issued about its own findings, not the full manuscript. The findings also highlight a gap in the toolkit: no vaccine currently exists for Epstein-Barr virus, and effective H. pylori vaccines remain limited despite decades of research.

What Comes Next for Prevention Efforts

IARC has framed the findings as an "enormous but largely preventable" burden, pointing to vaccination against HPV and hepatitis B, antimicrobial treatment such as H. pylori eradication and hepatitis C's direct-acting antivirals, and screening as tools that could avert a large share of it. Vaccination campaigns already show that this kind of prevention works in practice: CDC's own tracking of HPV vaccination's impact has found infections with the HPV types that cause most cancers and genital warts dropping sharply among vaccinated teens. The open question the analysis leaves for policymakers is access, since CDC guidance on preventing HPV-associated cancers and IARC's release both point to the same problem: the tools largely exist, but reach them unevenly, concentrated away from the low- and middle-income regions carrying most of this burden.

Common Questions

What is H. pylori and why is it linked to cancer? H. pylori is a bacterium that lives in the stomach lining; long-term infection is the best-established driver of stomach cancer, which is why the new analysis lists it as the single largest infection-linked cancer contributor worldwide, tied to 760,000 cases in 2024.

Can vaccines prevent infection-linked cancer? Yes, for two of the five infections identified: vaccines already exist against both HPV and hepatitis B, and IARC names vaccination as one of the main tools that could reduce this burden. No vaccine currently exists for Epstein-Barr virus, and H. pylori vaccines remain limited.

Where is the infection-linked cancer burden highest? Three-quarters of infection-attributable cancers occurred in low- and middle-income countries, with Eastern Asia alone accounting for 42% of the global total, driven mainly by H. pylori and hepatitis B, and Sub-Saharan Africa carrying a high burden driven by HPV, KSHV and HIV co-infection.

Is the full study available to read? The Lancet Oncology paper itself is behind a journal paywall. This article is based on its published abstract and on the official public statement IARC issued about its own findings, which report the same headline figures.

References

1. Eradication of Helicobacter pylori in the Primary Prevention of Gastric Cancer: A Systematic Review and Meta-Analysis. NIH. https://pmc.ncbi.nlm.nih.gov/articles/PMC12937033/
2. Impact of the HPV Vaccine | CDC. cdc.gov. https://www.cdc.gov/hpv/vaccination-impact/index.html
3. Preventing HPV-Associated Cancers | CDC. cdc.gov. https://www.cdc.gov/cancer/hpv/preventing-hpv-associated-cancers.html