Around one in eight of the world's cancer cases is likely caused by an infection. That is the striking finding of a major new analysis from the International Agency for Research on Cancer, published in The Lancet Oncology, which linked about 2.3 million of the 19.2 million new cancer cases diagnosed worldwide in 2024 to infections — and found that most of them trace back to just five pathogens.

Table of Contents

  1. The Five Main Culprits
  2. Why Poorer Countries Bear the Burden
  3. The Good News: Prevention Works
  4. How an Infection Becomes Cancer
  5. Key Takeaways
  6. Frequently Asked Questions
  7. Sources
  8. Read Next on Chronicle

The Five Main Culprits

Researchers analysed cancer data covering 12 infectious agents known to cause cancer, but five of them accounted for almost all infection-related cases, according to Medical Xpress:

  • Helicobacter pylori — a stomach bacterium spread through contaminated food and water — was the single largest contributor, linked to around 760,000 cases, mainly stomach cancer.
  • HPV (human papillomavirus) was associated with approximately 750,000 cases and is the main cause of cervical cancer, while also contributing to cancers of the throat, anus and genitals.
  • Hepatitis B was linked to about 360,000 cases, primarily liver cancer.
  • Epstein-Barr virus, best known for causing glandular fever, accounted for around 260,000 cases, including stomach cancers, nasopharyngeal cancers and lymphomas.
  • Hepatitis C was associated with approximately 160,000 cases, mostly liver cancer.

The study draws on data from the IARC Global Cancer Observatory and expands on previous research by including newly recognised infection–cancer links, such as recent evidence connecting Epstein-Barr virus with gastric cancer, per an iHeart analysis.

Why Poorer Countries Bear the Burden

The burden falls overwhelmingly on the developing world. Low- and middle-income countries accounted for about 77% of infection-related cancers, according to Medical Dialogues. Differences in infection prevalence, vaccination coverage, screening, testing and access to treatment are the likely drivers of the gap.

This geographic skew is the study's most urgent message: the cancers most tied to infection are concentrated precisely where the tools to prevent them are hardest to reach.

The Good News: Prevention Works

The authors stress that infection-related cancers are among the most preventable of all cancers. HPV and hepatitis B vaccination can sharply cut risk; cervical screening catches precancerous changes before they become dangerous; and although there is no hepatitis C vaccine, antiviral medicines cure most infections, Medical Dialogues reported.

Australia offers the proof of concept. Thanks to early HPV vaccination and a rapid shift to HPV-based screening, it is on course to eliminate cervical cancer by 2035 — the first country to achieve elimination through active measures, according to YourLifeChoices.

How an Infection Becomes Cancer

An infection does not mean cancer is inevitable — risk depends on whether the infection persists, the body's immune response, and other individual factors. But long-term infections can cause chronic inflammation or cellular damage that accumulates over years and eventually tips cells toward malignancy, per Medical Xpress.

The new paper builds on three decades of research by some of the same scientists, who previously estimated infection-attributable cancer for 1990, 2002, 2008, 2012 and 2018. The authors caution against comparing the new 12% figure directly with older estimates, because the sources and quality of the data have changed — the point of the new analysis is to show where controlling and preventing infections can cut cancer rates now, not to map a trend.

Key Takeaways

  • Infections caused about 2.3 million new cancer cases worldwide in 2024 — roughly 12%, or one in eight, according to a study in The Lancet Oncology.
  • Five pathogens cause almost all of them: H. pylori (760,000), HPV (750,000), hepatitis B (360,000), Epstein-Barr (260,000) and hepatitis C (160,000).
  • Low- and middle-income countries account for 77% of infection-related cancers.
  • HPV and hepatitis B vaccination, cervical screening and hepatitis C antivirals can prevent a large share of these cases.
  • Australia is on track to eliminate cervical cancer by 2035 through vaccination and HPV-based screening.

Frequently Asked Questions

Which infections cause the most cancers?

Helicobacter pylori, a stomach bacterium, is the single biggest contributor worldwide (around 760,000 cases), followed closely by HPV (750,000). Together with hepatitis B, Epstein-Barr virus and hepatitis C, these five pathogens cause nearly all infection-related cancers.

Can these cancers be prevented?

Yes. HPV and hepatitis B vaccines sharply reduce risk, cervical screening detects precancerous changes, and hepatitis C can be cured with antiviral drugs — preventing the liver damage that leads to cancer.

Why are poorer countries hit hardest?

About 77% of infection-related cancers occur in low- and middle-income countries, where infection rates are higher and vaccination, screening and treatment are less accessible.

Has the share of infection-caused cancers changed over time?

Earlier estimates ranged up to 18% (2002), but the researchers say the figures cannot be compared confidently because data sources and quality have changed. The new study's aim is prevention strategy, not trend analysis.

Sources

  • Medical Xpress — September 28, 2026: "One in eight cancers are likely caused by an infection worldwide, new study finds."
  • Medical Dialogues — October 2026: "Can Infections Cause Cancer? Lancet Study Links 1 in 8 Cancer Cases to Infections."
  • KJ97 (iHeart) — October 1, 2026: "One In Eight Global Cancer Cases In 2024 Linked To Infections."
  • YourLifeChoices — September 29, 2026: "The common infections linked to millions of cancer cases."

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