Infections accounted for about 1 in 8 new cancers worldwide in 2024, an estimated 2.3 million cases

Cancer is usually filed under lifestyle and bad luck: smoking, weight, age, genes. A large share of it belongs in a different drawer. According to an analysis published on September 28 in The Lancet Oncology, an estimated 2.3 million new cancer cases were attributable to infections globally in 2024, which is equivalent to 12% of all cancer cases. That is about one cancer in every eight.

The estimate comes from the International Agency for Research on Cancer, the World Health Organization’s cancer arm in Lyon, France, in work led by Harriet Rumgay and Gary Clifford. Its importance lies in what kind of cause an infection is. A bacterium can be cleared with antibiotics and a virus can be blocked by a vaccine, which is not true of age or inheritance.

How an infection can cause cancer

The agency keeps the world’s reference list of things known to cause cancer, and its top category, Group 1, is reserved for agents with sufficient evidence in humans. Thirteen infectious agents are on it. They include a stomach bacterium, Helicobacter pylori; the human papillomavirus, or HPV; the hepatitis B and C viruses (HBV, HCV); Epstein-Barr virus (EBV), which causes mononucleosis; HIV; and three parasitic worms.

They do their damage in different ways. Clifford told Newsweek that many of these infections “hijack the cellular machinery that controls the normal cell cycle in order to help their own replication”, and in doing so disable the systems that would normally repair a damaged cell or order it to die. Researchers who spoke to Newsweek also pointed to chronic inflammation and repeated tissue damage, which raise the chance of damage to a cell’s DNA.

Carrying the agent is rarely enough. Infection with EBV is almost ubiquitous in humans, the authors note, yet only a small minority of carriers develop one of the cancers it can cause.

How the 2024 estimate was calculated

The team did not follow patients. They combined two kinds of existing information. The first was the agency’s GLOBOCAN database, which estimates how many cancers of each type were diagnosed in each country in 2024. The second was the attributable fraction for each cancer, meaning the proportion of cases that would not have occurred without the infection.

Those fractions were primarily estimated from the prevalence of infection in people with cancer. For cervical cancer the fraction is 100%, because the disease does not arise without HPV. For stomach cancer outside the upper part of the organ it is 85%, and for the main type of liver cancer it is 52% for hepatitis B and 20% for hepatitis C.

The analysis covered 12 infectious agents classified as Group 1 carcinogens and 37 pairings of an infection with a cancer. The thirteenth agent on the list, hepatitis D virus, was added in 2025 and is not yet included. Sixteen of those pairings were new since the agency’s last global estimate, which found that 2.2 million infection-attributable cancer cases were diagnosed worldwide in 2018. HIV was counted for the first time, though only for a rare eye cancer, since the other cancers it promotes are already credited to HPV, Epstein-Barr virus or the Kaposi’s sarcoma virus.

Which infections caused the most cancer

Five agents accounted for nearly all of the total.

Infection	Estimated cancers in 2024	Main cancer caused
Helicobacter pylori	760,000	Stomach
Human papillomavirus (HPV)	750,000	Cervix
Hepatitis B virus	360,000	Liver
Epstein-Barr virus	260,000	Nose and throat (nasopharynx)
Hepatitis C virus	160,000	Liver
Kaposi’s sarcoma-associated herpesvirus	35,000	Kaposi’s sarcoma
Six other agents	19,000	Various

The largest number of cases was attributable to H. pylori, a bacterium that lives in the stomach lining. HPV was close behind, with 600,000 of its cases being cervical cancer and the rest cancers of the throat, anus and genitals in both sexes.

One ranking changed. EBV ranked as the fourth highest infectious cause of cancer globally, ahead of HCV in attributable cases. The virus has not become more dangerous. Evidence accumulated that it causes some stomach cancers and several lymphomas in addition to the nose and throat cancer long linked to it, so more cases are now assigned to it.

Men carried more of the burden than women for almost every agent. For all infectious agents other than HPV, rates were higher among males than females in all regions.

Where infection-related cancers are concentrated

Behind the global average lies a steep gradient. Infections lay behind 25% of all cancers in sub-Saharan Africa, 16% in southeastern Asia and 15% in eastern Asia. In northern Europe the share was 4%, and in North America 5%. Low- and middle-income countries accounted for 77% of all infection-attributable cancer cases.

Each region has its own pattern. Eastern Asia had the largest number of cases, 990,000, driven by H. pylori and hepatitis B, with China alone recording more of both than any other country. Sub-Saharan Africa had the highest proportional burden of cancer attributable to HPV, together with most of the world’s Kaposi’s sarcoma, a cancer of the cells that line blood and lymph vessels. Northern Africa’s burden was dominated by hepatitis C, almost all of it in Egypt. In the Americas and Europe, HPV and H. pylori led.

Patrick Moore, who holds a chair in cancer research at the University of Pittsburgh and was not involved in the study, offered Newsweek a comparison for scale. “This fraction, one in eight cancer patients, is the same fraction as lung cancer in all cancers in the U.S.,” Moore said.

What prevention of these infections has already shown

The case for acting on these numbers rests on evidence that removing the infection lowers the cancer rate, and for the two largest causes that evidence exists.

For HPV it comes from national vaccination. England began offering the vaccine to schoolgirls in 2008, and a registry study led by Milena Falcaro at King’s College London later compared cervical cancer rates in vaccinated and earlier cohorts. The relative reduction in cervical cancer rates by age at vaccine offer was largest in the youngest group: 87% for girls offered the vaccine at 12 to 13, against 34% for those offered it at 16 to 18. The authors concluded that the program has successfully almost eliminated cervical cancer in women born since Sept 1, 1995.

For H. pylori the evidence comes from randomized trials. Alexander Ford of the University of Leeds and colleagues pooled ten of them in the journal Gut. Among 8,323 healthy adults who carried the bacterium, a course of antibiotics roughly halved the number who later developed stomach cancer: eradication therapy reduced incidence of gastric cancer and reduced mortality from gastric cancer. About 72 people had to be treated to prevent one case. The trials were conducted in East Asian countries, where stomach cancer is common, and the benefit per person treated would be smaller where the disease is rare.

For hepatitis B there is a vaccine given in infancy, and for both hepatitis viruses there are antiviral drugs. For other agents there is no vaccine. The authors write that there has been little progress in developing H. pylori vaccines, while several clinical trials on EBV vaccines are ongoing.

Clifford told Newsweek that the results “demonstrate that a large fraction of cancers are caused by known infectious causes, and are thus preventable”. Which vaccines or tests apply to any one person depends on age, history and where they live, which is assessed by their doctor.

How firm the infection and cancer estimates are

These figures come from a model, and the paper is plain about its weak points.

The cancer counts depend on registries, and good registries are scarce where the burden is heaviest. The authors report that approximately 19% of the global population and only 2% of the population in Africa were covered by the high-quality registries that underpin the estimates. For the rest, numbers are extrapolated.

No range is attached to any estimate. The team writes that they could not identify a method to reliably estimate uncertainty intervals, given how many different data sources feed each figure, and chose to give single numbers over a false impression of precision. The 2.3 million is an approximation.

The total cannot be set against the 2.2 million reported for 2018 to show a trend. More infections and cancers are counted now and the registry data improved, and the authors state that comparisons with previous results are not possible because of changes in data sources and data quality over time.

There is also disagreement about whether the figure is too low. Only agents with settled evidence are included, so any infection whose role is still being established is left out. Karl Munger, a professor at Tufts University, told Newsweek the estimate was “lower than I would have expected. Other analyses have suggested that infection-associated cancers account for 15 to 20 percent of cancer cases globally”.

What the estimate changes for cancer prevention

Nothing in clinical guidance changes. The measures the authors call for, vaccination against HPV and hepatitis B, testing and treatment for H. pylori and the hepatitis viruses, cervical screening and HIV prevention, already exist. Their argument is about priorities: these strategies are known to be cost-effective and remain underused where they are needed most.

About one new cancer in eight worldwide begins with an infection that can mostly be prevented, detected or treated, on estimates that come with no margin of error and lean on sparse records in the regions most affected.