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In a worldwide estimate for 2024, infections were linked to about 2.3 million new cancer cases—roughly 12%, or one in eight. The leading contributor was Helicobacter pylori (H. pylori), narrowly ahead of HPV: the International Agency for Research on Cancer (IARC) estimated about 760,000 cases linked to H. pylori and about 750,000 to HPV. These are rounded, modeled population estimates, not predictions that an infected person will develop cancer.
What does “one in eight cancers” mean?
IARC’s analysis estimates that about 2.3 million new cancers worldwide in 2024 were attributable to infections. The study, published online in The Lancet Oncology on 28 September 2026, used 2024 cancer estimates from IARC’s Global Cancer Observatory and population-attributable fractions for 12 infectious agents classified as carcinogenic to humans. IARC’s announcement describes the global estimate; its study announcement gives further context.
“Attributable” describes an estimate across populations: it does not mean every cancer case in an infected person was caused by that infection, or that infection makes cancer inevitable. The figures are rounded estimates rather than exact case counts.
The total is not directly interchangeable with WHO’s older estimate that about 10% of cancers diagnosed globally in 2022 were attributed to carcinogenic infections. The estimates use different data years, and IARC says its newer analysis includes additional infectious agents, infection–cancer links, and cancer types.
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Which infections cause the largest number of cancers, and what types of cancer do they cause?
The five leading infections account for almost all infection-attributable cases in IARC’s 2024 analysis. Their estimated case totals and principal cancer links are:
| Infection | Estimated cancers attributable in 2024 | Main cancer links named by IARC |
|---|---|---|
| H. pylori | About 760,000 | Mainly stomach (gastric) cancer |
| HPV | About 750,000 | Predominantly cervical cancer; also anal, vulvar, vaginal, penile, and some head and neck cancers |
| Hepatitis B virus (HBV) | About 360,000 | Mostly liver cancer |
| Epstein–Barr virus (EBV) | About 260,000 | Largely nasopharyngeal cancer, as well as some stomach cancers and Hodgkin lymphoma |
| Hepatitis C virus (HCV) | About 160,000 | Mostly liver cancer |
All case totals in the table are IARC’s rounded estimates for 2024, published in 2026; they are not exact counts. IARC’s questions and answers identifies these leading agents and the cancers associated with them. H. pylori leads HPV by only about 10,000 in the rounded estimates, so the ranking is narrow rather than a large gap.
Rank #2
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Which other infections were included?
IARC assessed 12 agents in total. In addition to the five above, the analysis included Kaposi sarcoma-associated herpesvirus (KSHV), Schistosoma haematobium, human T-cell lymphotropic virus type 1 (HTLV-1), Opisthorchis viverrini, Clonorchis sinensis, Merkel cell polyomavirus, and HIV. The smaller totals for these agents are part of the overall estimate, but the available summary does not give their individual 2024 case counts.
Why are some regions more affected than others?
IARC identifies Eastern Asia, Sub-Saharan Africa, Central and Eastern Europe, and South-East Asia as regions with high infection-attributable cancer burdens. The leading infections differ by region: Eastern Asia’s burden is particularly associated with H. pylori and HBV, while Sub-Saharan Africa has a high burden of HPV-related cancers and substantial burden from HIV and KSHV.
More than three quarters of infection-related cancers occurred in low- and middle-income countries, according to IARC. Regional differences reflect infection prevalence, access to prevention and treatment, and wider social and economic conditions—not a single cause or uniform risk for everyone in a region.
What can prevent infection-related cancers?
There are established prevention and care measures, but which ones apply depends on the infection, a person’s circumstances, and local clinical guidance. IARC and WHO identify vaccination, testing and treatment, HIV prevention and care, and screening for HPV-related cancers as important tools.
- HPV: HPV vaccination and screening for HPV-related cancers, including cervical cancer. WHO describes HPV testing as a preferred cervical cancer screening method.
- HBV: Hepatitis B vaccination, along with testing and treatment where indicated.
- H. pylori, HCV, and HIV: Testing and treatment are among the approaches identified by IARC; HIV prevention and care also matter.
Vaccination, testing, treatment, and screening are not equally accessible or widely used everywhere. IARC points to financial, political, social, and health-system barriers. It describes vaccines against EBV, H. pylori, and KSHV as areas for investment—not as established, routinely available vaccines. Individual vaccination and screening recommendations vary by jurisdiction and clinical guidance; this global estimate does not determine what any one person needs.
Why does this ranking differ from older estimates?
Infection-attributable cancer estimates depend on the year of the cancer data and on which infection–cancer relationships are included. IARC says the 2024 analysis added infectious agents and 16 infection–cancer links, expanded cancer types associated with known agents, and incorporated recent evidence linking EBV with stomach cancer. Earlier estimates can therefore have different totals or rankings without either figure being a simple correction of the other.
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