About one in eight of all new cancers diagnosed worldwide — an estimated 2.3 million cases in 2024 — can be traced back to infections, according to the most comprehensive study of its kind yet. Published by the World Health Organization's cancer research arm, the analysis puts a common stomach bacterium ahead of HPV as the single biggest infection-driven cancer cause, and finds the burden falls overwhelmingly on poorer countries where prevention tools are hardest to reach.
Illustration: a stylized shield blocking infection-linked cancer risk.
What Happened
The International Agency for Research on Cancer (IARC), the World Health Organization's specialized cancer research agency, published a landmark analysis on September 28, 2026, in The Lancet Oncology estimating the global burden of cancers attributable to infections in 2024. Drawing on worldwide cancer figures from the IARC Global Cancer Observatory database, the researchers estimated how many new cancer cases could be traced back to 12 infectious agents classified as definite causes of cancer in humans.
The headline finding: an estimated 2.3 million new cancer cases in 2024 — about 12 percent of all new diagnoses worldwide, or roughly one in eight — were attributable to infections. Five pathogens accounted for nearly the entire burden: the bacterium Helicobacter pylori with an estimated 760,000 cases, human papillomavirus (HPV) with about 750,000 cases, hepatitis B virus with roughly 360,000 cases, Epstein-Barr virus with around 260,000 cases, and hepatitis C virus with about 160,000 cases. More than 20 different cancer types were linked to these infections, from stomach and cervical cancers to liver cancers and lymphomas.
The biggest surprise, widely noted in coverage of the study, was that a stomach bacterium — H. pylori, commonly associated with stomach ulcers — was linked to slightly more cancer cases worldwide than HPV, the virus famous for its connection to cervical cancer. The analysis also newly established the role of additional agents, including HIV and the Merkel cell polyomavirus, and incorporated newer evidence such as the recently recognized link between Epstein-Barr virus and gastric (stomach) cancer.
"The findings underscore the major role that infection control can play in reducing the global cancer burden," said Dr. Harriet Rumgay, a scientist in the Cancer Surveillance Branch at IARC and a co-author of the article, in the agency's press release. "Despite progress in vaccination and screening, infection-related cancers remain a major global challenge, with the burden falling disproportionately on populations in low- and middle-income countries."
Illustration: a stylized view of vaccines blocking cancer-causing germs.
Background
The idea that infections can cause cancer is not new — scientists have long known that chronic infection can raise cancer risk through persistent inflammation, cell damage, or weakening of the immune system, as the American Cancer Society explains. What the new IARC analysis does is put the most complete, up-to-date numbers on the phenomenon yet, expanding the list of agents studied and the cancer types counted.
The researchers examined 12 infectious agents that are classified as Group 1 carcinogens — agents with definite evidence of causing cancer in humans. These include viruses (HPV, hepatitis B, hepatitis C, Epstein-Barr virus, HIV, Kaposi sarcoma-associated herpesvirus and others), a single bacterium — H. pylori, which the American Cancer Society calls the only bacterium with strong links to cancer — and certain parasites. The team then used prior research on how strongly each infection is associated with specific cancers to estimate attributable cases worldwide.
The global cancer burden has been rising sharply overall: about 20 million new cancer cases were diagnosed worldwide in 2024, according to the same underlying estimates. Against that backdrop, infection-attributable cancers represent one of the most preventable slices of the total — because many of the infections involved can be prevented, detected, or treated with tools that already exist.
The study also highlights a troubling inequality. More than three-quarters of infection-related cancers occurred in low- and middle-income countries, where access to preventive care and treatment is often limited. Eastern Asia alone accounted for roughly 990,000 infection-attributable cases in 2024 — about 42 percent of the global total — with an age-standardized incidence rate of 31.9 cases per 100,000 people, against a worldwide average of 22.7. Sub-Saharan Africa accounted for roughly another 28.5 percent of cases, and central and eastern Europe and south-eastern Asia also sat above the global average.
Why It Matters
Millions of cancer cases each year are, in principle, avoidable — not through futuristic gene therapy, but through vaccines, antibiotics and screening that already sit on clinic shelves. HPV and hepatitis B vaccines already prevent infection with two of the five biggest cancer-causing pathogens; antibiotics can eliminate H. pylori; hepatitis C now has curative therapy; and screening programs can catch cervical cancers early. Senior author Gary Clifford put it bluntly: "We can intervene before it gets anywhere near cancer… Prevention works."
But the study's authors caution that the gap between what is possible and what is happening remains vast. Real-world impact is limited by vaccine hesitancy, cuts to development aid, weak health systems, and gaps in screening coverage — and crucially, no effective vaccines yet exist for Epstein-Barr virus or H. pylori, making the authors' call for new prevention tools an urgent research priority.
Context matters for individuals too. Having one of these infections does not automatically mean developing cancer — the overwhelming majority of people with these infections never do, and cancer is not contagious in the usual sense. The risk is population-level: the infections, under particular biological circumstances, raise the odds of specific cancers. The practical message, the authors say, is prevention: staying up to date on recommended vaccines, attending cancer screening programs, and seeking testing and treatment where appropriate.
The study lands in a busy stretch for global public health. Just this month, WHO launched new guidelines on October 7, 2026, for the integrated management of obesity in children and adolescents — a response to an estimated 400 million children and adolescents aged 5–19 being overweight in 2024, including 170 million living with obesity, a figure that has quadrupled since 1990. Earlier in October, WHO also reported that global life expectancy has bounced back to near pre-pandemic levels, while warning that drug-use disorders and other non-communicable risks continue to climb.
Illustration: a stylized world map of the uneven global cancer burden.
What Happens Next
- Researchers are expected to push the EBV-vaccine effort forward, with the IARC authors explicitly calling for investment in vaccines against Epstein-Barr virus and H. pylori, for which no effective vaccines exist.
- Countries with the highest infection-attributable burdens — led by Eastern Asia, sub-Saharan Africa, and central and eastern Europe — face pressure to expand HPV and hepatitis B vaccination coverage, H. pylori testing and treatment, and cervical screening.
- WHO and national health agencies will weigh how the new burden estimates feed into cancer-control targets and funding priorities, particularly for low- and middle-income countries that carry more than three-quarters of the cases.
- Health researchers are watching whether expanded screening and treatment can cut the infection-driven share of the roughly 20 million annual new cancer cases over the coming decade.
- The study's methods are likely to be applied to future years, giving the world a regular scorecard on how much of the cancer burden is preventable through infection control.
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FAQ
Q: What did the WHO cancer study actually find?
A: The International Agency for Research on Cancer estimated that about 2.3 million new cancer cases worldwide in 2024 — roughly 12 percent, or one in eight, of all new diagnoses — were attributable to infections, based on the agency's Global Cancer Observatory database.
Q: Which infections cause the most cancers?
A: Just five agents account for nearly all infection-linked cancers: Helicobacter pylori (~760,000 cases), HPV (~750,000), hepatitis B (~360,000), Epstein-Barr virus (~260,000) and hepatitis C (~160,000), across more than 20 cancer types.
Q: Does having one of these infections mean I will get cancer?
A: No. The vast majority of people with these infections never develop cancer, and cancer is not contagious in the usual sense. The study measures population-level risk — these infections raise the odds of specific cancers under particular circumstances.
Q: Can infection-related cancers be prevented?
A: Many can. Vaccines already protect against HPV and hepatitis B, antibiotics can eliminate H. pylori, hepatitis C has curative therapy, and screening catches some cancers early. The authors flag the need for new vaccines against Epstein-Barr virus and H. pylori, which do not yet exist.
Q: Where is the burden heaviest?
A: More than three-quarters of infection-related cancers occur in low- and middle-income countries. Eastern Asia alone accounted for about 990,000 cases in 2024 (42% of the global total), with sub-Saharan Africa contributing roughly another 28.5%.
Sources
- IARC / WHO press release, Lyon, France (Sept 28, 2026) — "One in eight cancers worldwide linked to infections": 2.3 million infection-attributable new cases in 2024, 12 agents studied, published in The Lancet Oncology, co-authors Harriet Rumgay and Gary Clifford.
- The Lancet Oncology (Sept 2026) — IARC analysis of the global burden of cancer attributable to infections in 2024, based on IARC Global Cancer Observatory data.
- The Healthy (Oct 16, 2026) — coverage of the IARC findings: breakdown of the five leading agents and prevention tools.
- WHO (Oct 7, 2026) — launch of guidelines on the integrated management of obesity in children and adolescents: 400 million children and adolescents overweight in 2024, 170 million with obesity.
- UN News (Oct 2, 2026) — WHO: global life expectancy bounces back to near pre-pandemic levels.
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