One in Eight Cancer Cases Worldwide Caused by Infections, Study Finds

About 2.3 million new cancer cases diagnosed worldwide in 2024 — roughly one in every eight — were caused by infections, according to a major international analysis published Sept. 28 in The Lancet Oncology. The researchers' blunt message: most of those cancers were preventable with tools that already exist, from vaccines to testing and treatment.

A doctor places a bandage on a teenage patient's arm after she received an immunization, in a photo from the American Academy of Pediatrics' HPV vaccine campaign.

When people think about what causes cancer, they usually picture smoking, sun exposure, or bad genetic luck. But one of the largest causes of the disease has been hiding in plain sight: germs. Viruses, bacteria, and parasites quietly triggered an estimated 2.3 million new cancers in a single year — about 12 percent of the roughly 20 million cancers diagnosed globally in 2024.

The analysis, titled "Global burden of cancer attributable to infections in 2024: a worldwide incidence analysis," was led by researchers at the International Agency for Research on Cancer (IARC), the World Health Organization's specialized cancer agency. Using the Global Cancer Observatory's GLOBOCAN 2024 database, the team mapped 12 infectious agents that IARC classifies as Group 1 carcinogens — organisms confirmed to cause cancer in humans — and combined that with global infection data to estimate how many cancers each one caused.

The point of the exercise was not just to count. It was to show how much of the world's cancer burden could be avoided. According to reports on the study, infections do not make cancer inevitable: whether an infection turns into cancer depends on factors such as whether it persists in the body, the person's immune response, and other individual risks. But long-running infections can cause chronic inflammation and cellular damage that, over years or decades, can push cells toward malignancy.

The Five Infections Behind Most Cases

A handful of familiar microbes did the overwhelming majority of the damage. According to the analysis, five pathogens accounted for nearly all infection-linked cancers:

Helicobacter pylori, a bacterium that infects the stomach lining, was the single largest contributor, linked to about 760,000 cases — mostly gastric (stomach) cancers. The infection can spread through saliva or contaminated food and water, and it is treatable with antibiotics and stomach-acid medications.

Human papillomavirus (HPV) was close behind with roughly 750,000 cases. HPV is the main cause of cervical cancer, but it also drives cancers of the penis, throat, mouth, and anus.

Hepatitis B virus (HBV) was tied to about 360,000 cases, mostly liver cancer. The Epstein-Barr virus (EBV) — the virus that causes mononucleosis — was linked to around 260,000 cases, including throat (nasopharyngeal) cancers, certain lymphomas, and some stomach cancers. Hepatitis C virus (HCV) accounted for roughly 160,000 more, also mostly liver cancer.

The study also added new links to the cancer-causing roster, including HIV and the Merkel cell polyomavirus, and confirmed the recently established connection between the Epstein-Barr virus and gastric cancer. A focused analysis of EBV revealed that the types of cancer it drives vary significantly by region.

Where the Burden Falls Hardest

The geography of infection-driven cancer is strikingly uneven. Eastern Asia carried the heaviest absolute burden — about 990,000 cases, or 42 percent of the global total — with an age-standardized incidence rate of 31.9 per 100,000 people.

But the highest rate per person was in sub-Saharan Africa, at 28.5 cases per 100,000, above the global average of 22.7. Central and Eastern Europe (24.3) and Southeastern Asia (23.1) also exceeded the global average.

Low- and middle-income countries accounted for about 77 percent of all infection-attributable cancer cases. Researchers attribute the gap to differences in infection prevalence, vaccination coverage, and access to screening, testing, and treatment — and to sparse cancer-registry data in the poorest regions, which may mean the true toll is even larger.

A Prevention Gap That Costs Millions

What makes these numbers especially painful is that the weapons against them already exist. The study's authors point to HPV and hepatitis B vaccination, testing and treatment for HIV, H. pylori, hepatitis B and hepatitis C, safe injection practices, condoms and pre-exposure prophylaxis (PrEP) against HIV, and screening for precancerous lesions in HPV-driven cervical and anal cancer.

Yet global uptake is far below target. In 2024, only 31 percent of eligible adolescent girls worldwide had received even one dose of the HPV vaccine — far short of the World Health Organization's 90 percent goal.

Where vaccination has taken hold, the results are dramatic. Dr. Rebecca Perkins, an obstetrician-gynecologist at Tufts University School of Medicine, told reporters that cervical cancer is now starting to disappear in countries that pushed vaccination rates above 80 percent, with research from Australia, England, and Finland showing no cases of HPV-related cancers or deaths among young adults vaccinated by age 13.

Infectious disease specialist Dr. Alex Lazo-Vasquez added that hepatitis B and hepatitis C infections can go unnoticed for decades before eventually leading to liver cancer — a silent window in which testing and treatment could intervene.

Vials of recombinant hepatitis B vaccine beside a syringe. The study lists hepatitis B vaccination among the proven tools that could prevent hundreds of thousands of cancer cases.

What This Means

The study lands as a challenge to how the medical world is organized. "We have historically siloed infectious diseases and oncology, but they are deeply intertwined," said Dr. David Greenberg, medical director of hematology oncology at Hackensack Meridian Jersey Shore University Medical Center. He called the Lancet findings "a profound reminder that a significant portion of our global cancer burden is fundamentally preventable," arguing that "by shifting our focus toward aggressive infection control, we can literally vaccinate and treat our way out of millions of future cancer diagnoses."

The findings also sharpen the investment case for research and development into new prevention tools — most notably vaccines against the Epstein-Barr virus, for which no vaccine currently exists. As the study's authors put it, infection control is cancer control.

There is also a data problem. The heaviest burdens fall on regions with the weakest cancer surveillance, meaning the map of infection-driven cancer has blind spots exactly where the disease hits hardest. Better registries and research in Africa and low-income countries are needed to fully understand — and then reduce — the toll.

A doctor consults with a patient during a cancer-screening visit, in a photo from the Southern Cancer Center's Pap-test information page.

What Happens Next

The WHO has set an elimination target for cervical cancer — 90 percent of girls vaccinated, 70 percent of women screened, 90 percent of those with disease treated — but the current 31 percent HPV coverage shows how far the world is from that goal. Expanding HPV and hepatitis B vaccination, scaling up screening for precancerous lesions, and making testing and treatment for H. pylori and hepatitis widely available are all proven, cost-effective steps.

For individuals, the takeaway is practical rather than alarming: infection-linked cancers are among the few cancers with clear, actionable prevention. Vaccination, safe practices, and routine screening turn what the study frames as a tragedy of neglect into a tractable public-health target.

Millions of cancers a year, the researchers argue, are not inevitable. They are the price of infections left unprevented — and the bill, at last count, runs to 2.3 million cases annually.