A study published Monday in The Lancet Oncology has found that infections account for one in eight cancer cases around the world. Researchers estimate that viruses, bacteria and other microbes were responsible for roughly 2.3 million new cancer diagnoses in 2024, which represents about 12 per cent of all new cancer cases globally.
Researchers at The International Agency for Research on Cancer (IARC), which is part of the World Health Organization, carried out cbc.ca’s study. What they found is that infections play a much larger role in causing cancer than most people understand.
Helicobacter pylori leads the count
Globally, Helicobacter pylori was the leading cause of cancer cases, with 760,000 instances recorded, and it is particularly prevalent in eastern Asia. The bacterium raises the risk of stomach cancer.
Nearly 750,000 new cases of HPV, the human papillomavirus, emerged globally. It accounts for 100 per cent of cervical cancer cases and also anal, vulvar, vaginal, penile and some head and neck cancers. The rates were highest in sub-Saharan Africa.
A significant number of liver cancer cases were tied to hepatitis B virus (HBV) and hepatitis C virus (HCV).
New cancers added to the list
Researchers have now tied a larger set of cancers to infections, adding 16 more to their existing list. Among the new additions is HIV and its connection to cervical cancer, along with a very rare virus known as Merkel cell polyomavirus, which has been shown to cause an aggressive form of skin cancer.
Since earlier tallies were made, the body of research has expanded considerably. Gary Clifford, a cancer epidemiologist and study co-author based in Lyon, France, said the science has come a long way.
“There’s been new infectious agents identified in this time as being cancer-causing, and even the infectious agents that we knew about in the past, the evidence has increased about the number of different cancers that they can cause,” he said.
Epstein-Barr’s growing burden
A notable change involves the acknowledgment of Epstein-Barr virus (EBV) and its role in cancer. In 2024, EBV was tied to roughly 260,000 cases worldwide. It has also been associated with nasopharyngeal cancer, certain gastric cancers, and Hodgkin’s lymphoma.
“That’s quite a big burden of cancer caused by Epstein-Barr virus that was not counted in the past, but is now recognized,” Clifford said.
EBV plays a major role in the development of multiple sclerosis, and unlike many other infections with available vaccines or antibiotic treatments, there are no tools to fight against it.
“The fact that we’re seeing Epstein-Barr has caused all these chronic diseases — it’s increasingly becoming a target that people need to focus on for prevention,” he said.
Global gaps in prevention
The report draws attention to wide regional differences, largely stemming from past inequalities. Nations with high incomes that set up cancer screening and vaccination programs over the past few decades are faring much better than lower- and medium-resourced countries, where access to prevention and treatment remains limited.
“We really still have a lot of work to do implementing things that we know work and we’ve known for a long time but haven’t really made it into all populations in the world,” Clifford said.
Canada’s numbers
In Canada, the picture is different. According to a 2019 study, the rate of cancers attributable to infections was estimated to be at four per cent. Karena Volesky, an epidemiologist in Montreal, led the Canadian research team while at McGill University.
“It tells us how important each of the 12 infections are,” Volesky said of the new global numbers.
Though these kinds of infections occur less often in Canada, her research found they result in over 7,000 cancer diagnoses annually.
HPV and the cervical cancer plateau
The virus that causes human papillomavirus spreads through sexual contact, while the HPV vaccine offers protection against the most common forms of infection that can lead to cancer. In Canada, cervical cancer rates had been falling steadily thanks to strong childhood vaccination programs, though they stopped dropping last year.
The director of health policy at the Canadian Cancer Society is Elizabeth Holmes, who said “That’s certainly a concern — that we might not meet our goal of elimination of cervical cancer by 2040 unless those rates start to decline again,”.
The goal of Canada’s plan to end cervical cancer is threefold: it calls for vaccination coverage to reach 90 per cent, screening participation to rise to 90 per cent, and prompt followup care following screening.
“Right now, only about five provinces are above 80 per cent, and I think at least one is as low as 66 per cent,” Holmes said.
The stomach bacteria problem
Helicobacter pylori, a bacterium first identified in the early 1980s, causes more cancer cases than any other infection, and its main target is the stomach. The research found the greatest disease toll in eastern Asia, particularly in nations such as Japan, South Korea and China. But this is not just a distant problem; it affects us here as well.
“It’s a horrible disease to die from,” said Dr. Paul Moayyedi, a leading researcher and gastroenterologist at McMaster University. About 2,000 Canadians die every year from stomach cancer.
The doctor is calling for a widespread testing program aimed at detecting the germ, which can be found using a blood or breath test, stool sample or endoscopy, and then treated.
The takeaway
The study shows that infections are a major contributor to cancer worldwide. The numbers are stark: 1 in 8 cancer cases, 2.3 million new cases in 2024, 12 per cent of all new cases.
The spread of the condition is not equal at all. Wealthier nations have advanced by catching it early and vaccinating. Poorer and moderately resourced countries fall far behind.
Clifford stated his position directly: “We really still have a lot of work to do implementing things that we know work.”
The message is straightforward: infections lead to cancer. We know which ones they are. We know how to prevent them. The real issue is whether the entire world can put that knowledge into practice across all its communities.
Key facts
- 1 in 8 cancer cases worldwide are caused by infections
- 2.3 million new cancer cases in 2024 linked to infections (12 per cent of all new cases)
- Helicobacter pylori: 760,000 cases, predominantly in eastern Asia
- HPV: nearly 750,000 new cases globally, highest in sub-Saharan Africa
- EBV: 260,000 cases globally in 2024
- Canada: 4 per cent of cancers attributable to infections (2019 study)
- Canada: more than 7,000 cancer diagnoses each year linked to infections
Source material: “1 in 8 cancer cases worldwide are caused by infections, study finds,” cbc.ca.
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