Topicsinfections that cause cancercan infections cause cancerHPV cancer riskH. pylori stomach cancerhepatitis B liver cancerEpstein-Barr virus cancerhepatitis C liver cancercervical cancer vaccinestomach cancer causesIARC Lancet Oncology cancer study
A nurse administers the HPV vaccine in Washington, DC — vaccination is the main line of defense against infections that cause cancer
Vaccination in Washington, DC. HPV and hepatitis B vaccines are among the most powerful — and most underused — cancer prevention tools in existence. Photo: Ted Eytan, via Wikimedia Commons (CC BY-SA 2.0).

Infections that cause cancer are far more common than most people realize. A sweeping new analysis from the International Agency for Research on Cancer (IARC), the World Health Organization's cancer research arm, estimates that about 2.3 million new cancer cases diagnosed worldwide in 2024 — roughly one in eight, or 12 percent of the global total — were attributable to infections. Published in The Lancet Oncology, the study is the most comprehensive assessment yet of a truth oncology has wrestled with for decades: a large share of the world's cancers are not a matter of bad genes or bad luck, but of pathogens we can already fight.

Five infectious agents account for nearly all of those 2.3 million cases. The stomach bacterium Helicobacter pylori is the single largest contributor, linked to an estimated 760,000 cases, mainly stomach cancer. Close behind is human papillomavirus (HPV), with about 750,000 cases — virtually all of the roughly 600,000 cervical cancers diagnosed that year, plus cancers of the anus, vulva, vagina and penis and some head-and-neck cancers. Hepatitis B virus drove some 360,000 cases, mostly liver cancer; the Epstein-Barr virus, the bug behind mononucleosis, accounted for about 260,000, including nasopharyngeal cancers, Hodgkin lymphoma and some stomach cancers; and hepatitis C added roughly 160,000, almost all of them liver cancers. Seven further proven carcinogenic infections make up the remainder of the twelve agents IARC classifies as definite causes of cancer in humans.

Why this matters: these are the most preventable cancers on Earth

Cancer is usually framed as a problem of detection and treatment — better scans, better drugs, better surgery. The IARC numbers reframe it as a problem of prevention we are already losing for no good reason. HPV vaccines and hepatitis B vaccines exist, are safe, and have been in use for decades. Curative antivirals can wipe out hepatitis C. Cervical screening catches HPV damage years before it turns malignant. As the study's authors put it, many of these 2.3 million cancers could have been prevented through vaccination, treatment or screening — the tools are on the shelf; the failure is in getting them to the people who need them.

The real story here is not the biology, which researchers have understood for years, but the distribution. Roughly 77 percent of infection-linked cancers strike low- and middle-income countries. The same cervical cancer that is becoming rare in Australia — where a national HPV vaccination program launched in 2007 cut infections by 90 percent among the eligible and put the country on track to eliminate the disease by 2035 — still kills hundreds of thousands of women a year in places where the vaccine never arrived. That gap is a policy choice, not a scientific mystery, and it is widening: vaccine hesitancy, cuts to development aid and fragile health systems are all slowing the very programs that would close it, the IARC and WHO authors warn.

Put in dollars and lives, the arithmetic is brutal. Treating late-stage cervical or liver cancer costs health systems vastly more than a two-dose vaccine course, yet prevention budgets are the first cut when money is tight. Every percentage point of HPV or hepatitis B coverage bought today is a cohort of cancers that will never need treatment in twenty years — the cheapest oncology program ever devised, and the one the world funds least consistently.

Can infections cause cancer? The five culprits, and how they do it

Yes — and the mechanisms are now well mapped. H. pylori does its damage the slow way: decades of chronic inflammation in the stomach lining, as the immune system's long war with the bacterium steadily raises the odds of a malignant mutation. HPV works more directly: its E6 and E7 oncoproteins disable the cell's tumor-suppressor brakes, p53 and Rb, letting infected cervical cells divide unchecked. Hepatitis B and C grind the liver down through chronic hepatitis and cirrhosis until, in a fraction of carriers, a hepatocellular carcinoma emerges — hepatitis B is linked to about half of all hepatocellular carcinomas, hepatitis C to about a fifth. Epstein-Barr virus hides in B cells in a latent state, periodically driving the proliferation that can tip into Burkitt lymphoma, Hodgkin lymphoma or nasopharyngeal cancer — EBV is linked to 88 percent of nasopharyngeal cancers, a tumor of the upper throat behind the nose.

The study's notable new finding concerns EBV and the stomach. Recent evidence has firmed up the link between Epstein-Barr virus and gastric cancer, one of the 16 additional infection-cancer associations added since IARC's last such assessment in 2018. The update also folded in HIV and Merkel cell polyomavirus and expanded the list of cancer sites tied to hepatitis B and C, Kaposi sarcoma-associated herpesvirus and EBV. The remaining agents on the twelve-strong list — Schistosoma haematobium, HTLV-1, the liver flukes Opisthorchis viverrini and Clonorchis sinensis — contribute smaller but locally devastating totals, particularly in parts of Africa and Southeast Asia.

Background: a Nobel Prize for stomach bacteria and a vaccine against cancer

The idea that infections cause cancer was once career-threatening heresy. When Barry Marshall and Robin Warren proposed in the 1980s that a spiral bacterium caused gastritis and ulcers, the medical establishment dismissed them — until Marshall famously swallowed a culture of H. pylori, gave himself gastritis, and cured it with antibiotics. The Nobel Prize in Physiology or Medicine followed in 2005. H. pylori is now classified by IARC itself as a definite carcinogen, and its discovery rewrote the oldest story in oncology: that stomach cancer was simply fate.

The HPV story moved faster but landed harder. The vaccine's approval in 2006 gave humanity its first shot that prevents cancer rather than treating it. Australia's school-based program became the proof of concept the world needed: within years, genital warts and precancerous lesions collapsed among the vaccinated, and the country is now plausibly on course to eliminate cervical cancer as a public health problem by 2035. The cautionary footnote is that even Australia has slipped — vaccination among 15-year-olds fell from 85.7 percent in 2020 to 79.5 percent in 2024, below the 90 percent target the WHO and Australia set for 2030. If coverage erodes where delivery is easy, imagine the fragility where it is hard.

Hepatitis B vaccination has quietly been one of public health's greatest victories — a birth dose followed by infant immunization has driven childhood HBV infection to historic lows in countries that adopted it. Hepatitis C is the mirror image: no vaccine exists, but direct-acting antivirals now cure the infection outright, which means test-and-treat programs can delete future liver cancers one cured patient at a time. EBV, by contrast, remains the frontier: no vaccine yet, though several candidates are in the pipeline — and this study's authors flag an EBV vaccine as an urgent research priority.

Electron micrograph of Helicobacter pylori, the stomach bacterium linked to about 760,000 cancer cases in 2024
Electron micrograph of Helicobacter pylori, the largest single infectious contributor to the global cancer burden. Image: Yutaka Tsutsumi, M.D., Fujita Health University School of Medicine, via Wikimedia Commons.

H. pylori and stomach cancer: the bacterium behind 4 percent of all cancers

H. pylori deserves its grim top ranking examined closely, because it is also the strangest case on the list. Roughly half the world's population carries the bacterium, most of them without symptoms — yet it accounts for about 4 percent of all cancers diagnosed on the planet. The gap between ubiquitous infection and relatively rare malignancy is where the nuance lives: strain differences matter, host genetics matter, diet and co-infections matter, and the bacterium's slow decline in wealthy countries — through sanitation and incidental antibiotic use — has coincided with a long fall in stomach cancer rates there.

That makes H. pylori a disease of development in reverse: the places industrializing fastest often carry the heaviest H. pylori burden and the weakest endoscopy infrastructure to catch the cancers it causes. Test-and-treat strategies — screening for the bacterium and eradicating it with antibiotics — are cheap and effective, but they require a primary-care system that can find asymptomatic people and follow up. There is no H. pylori vaccine, and the antibiotic regimens are getting harder as resistance spreads — another reason the prevention window needs to be used while it is open.

Who carries the burden: 77 percent of cases in poorer countries

The geography of infection-linked cancer is the geography of inequality. East Asia accounts for about 42 percent of the world's infection-attributable cancers and sub-Saharan Africa for about 28.5 percent. Southeast Asia's share of cancers linked to infections runs at 16 percent, versus 12 percent globally — including some 27,000 EBV-linked nasopharyngeal cancers, four-fifths of the region's EBV total. India alone is estimated at roughly 190,000 infection-linked cases in 2024. Eastern Asia, sub-Saharan Africa, Central and Eastern Europe and Southeast Asia carry the highest shares.

These are not mysterious patterns. They track vaccination coverage, screening access, sanitation and the strength of primary care — in other words, money and organization. "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," said study co-author Dr. Harriet Rumgay, a scientist in IARC's Cancer Surveillance Branch in Lyon, in the agency's release. The uncomfortable corollary: the high-income world has largely solved this problem for itself and left the solution on the shelf for everyone else.

There is also a warning for wealthy countries inside the data. HPV vaccination rates are softening in several high-income settings, and hepatitis C — curable, remember — still circulates widely among under-screened populations. Complacency is the one risk factor no vaccine covers.

What the numbers don't say: infection is not destiny

Serious caveats apply, and the authors state them plainly. The 2.3 million figure is built from population-attributable fractions — statistical estimates that combine infection prevalence with cancer risk — not from tracking individual patients from infection to tumor. That makes the totals only as good as each country's cancer registry and infection surveillance, and data quality varies enormously. The study also includes only infections already proven to cause cancer, which means the true infection-linked share could be larger, not smaller: unknown or suspected links are excluded by design.

Nor does infection equal inevitability. The overwhelming majority of HPV infections clear on their own; most H. pylori carriers never develop cancer; most hepatitis B infections acquired in adulthood resolve. Persistence, viral strain, immune status and co-factors — smoking with HPV-driven head-and-neck cancer, alcohol with hepatitis-driven liver cancer — decide who progresses. That is precisely why screening matters as much as vaccination: it finds the persistent infections and precancers in time.

One more caution for the historically minded: this is the sixth such IARC assessment, following estimates for 1990, 2002, 2008, 2012 and 2018, and the headline share has bounced around — it was as high as 18 percent in 2002. The authors stress those figures cannot be confidently compared, because the data sources and methods changed each time. The 2024 number is a snapshot, not a trend line — and its purpose is practical, not historical: to show where infection control can cut cancer rates now.

Outside experts not involved in the work say the message for clinicians is direct. "Hopefully these data can help remind physicians that [infection-related] cancers are an important cause of mortality that they have tools to address in some, but not all, cases," said Nina R. Salama of the Fred Hutchinson Cancer Center in Seattle, who studies H. pylori.

A cancer researcher pipetting in the laboratory; the IARC analysis drew on 2024 data from the agency's Global Cancer Observatory
Laboratory research underpins the IARC estimates, which draw on 2024 data from the agency's Global Cancer Observatory covering 36 cancer types. Photo: Diane A. Reid, via Wikimedia Commons (public domain).

What happens next: vaccines, screening and Europe's new anti-cancer code

The prevention playbook is written; the question is scale. The fifth edition of the European Code Against Cancer — released just as the IARC numbers landed — puts vaccination and early diagnosis at the center of its recommendations, a signal that Europe intends to treat infection-linked cancers as a systems problem rather than a series of individual tragedies. The WHO's cervical cancer elimination strategy sets the concrete target: 90 percent of 15-year-old girls vaccinated against HPV by 2030, alongside screening and treatment goals.

Three moves would change the curve fastest. First, close the HPV vaccine gap: the doses exist, the cold chain exists, and school-based delivery has been proven from Kigali to Canberra — what is missing is sustained financing and political will, particularly as development aid contracts. Second, universal hepatitis B birth-dose vaccination plus adult test-and-treat for hepatitis C, which converts a cancer pipeline into a curable infection. Third, screening at scale: HPV DNA testing, now the WHO's preferred cervical screening method, and H. pylori test-and-treat in high-burden regions.

The pipeline offers longer-term hope. EBV vaccine candidates are advancing, and success there would attack a quarter-million annual cancers at the source. H. pylori vaccine research continues, though nothing is near licensure. And the therapeutic frontier — from personalized mRNA cancer vaccines to better immunotherapies — will matter enormously for the cancers prevention misses. But the deepest lesson of the IARC study is humbler: the most powerful anti-cancer technology of the next decade is not a new drug. It is the needle, the screening swab and the antibiotic course — delivered everywhere, not just where they are already routine.

More from World and Health

Sources

Reporting basis: Case counts, shares and regional breakdowns are from the IARC analysis published online September 28, 2026 in The Lancet Oncology (DOI: 10.1016/S1470-2045(26)00307-4), based on 2024 estimates from the IARC Global Cancer Observatory covering 36 cancer types. Figures are population-attributable estimates, not individually tracked cases, and are rounded as reported by IARC and secondary outlets.

World / Health · Published October 4, 2026Back to World