One in Eight New Cancers Worldwide Caused by Infections, WHO Agency Says, With H. Pylori and HPV Topping List

LYON, France — About one in eight new cancer cases worldwide is caused by an infection, according to a new analysis from the World Health Organization's cancer research agency, which researchers say highlights the potential to prevent millions of cancers through vaccination, screening and treatment.

The study by the International Agency for Research on Cancer, published in The Lancet Oncology, estimated that 2.3 million new cancer cases in 2024, about 12% of all new diagnoses, were caused by infections. 2024 is the most recent year for which data were available.

The researchers examined 12 infectious agents known to cause cancer, using data from the agency's Global Cancer Observatory database.

Bacteria and viruses lead the burden

The largest share of infection-related cancers was linked to Helicobacter pylori, a bacterium that infects the stomach. H. pylori was responsible for an estimated 760,000 cancer cases in 2024, primarily stomach cancers.

Human papillomavirus, or HPV, followed closely with about 750,000 cases. Certain strains of HPV cause the majority of cervical cancers, as well as a number of head and neck cancers, said Harriet Rumgay, an epidemiologist at the agency and an author of the report.

Hepatitis B accounted for about 360,000 cases and hepatitis C for about 160,000, mostly liver cancers. Doctors have known for decades that both viruses drive many liver cancer cases.

Epstein-Barr virus, which causes mononucleosis and infects more than 90% of the world's population, was linked to about 260,000 cases. Those included lymphomas, nasopharyngeal cancers and stomach cancers.

Seven other infections, including HIV and Merkel cell polyomavirus, were also identified as cancer-causing agents in the analysis.

Most infected people won't develop cancer

Experts emphasize that most people who carry these infections will never develop cancer. When cancer does occur, it can take years to develop, and infection is often only one of several contributing factors.

In the case of Epstein-Barr virus, for example, researchers believe genetic predisposition and environmental factors also play a role in relatively high rates of virus-linked nasopharyngeal cancers in China.

How infections cause cancer

The mechanisms vary by infection. HIV weakens the immune system, making it easier for other cancer-causing viruses to multiply. H. pylori damages tissue and produces toxins that disrupt the body's normal control of cell growth and division.

Epstein-Barr virus hides inside immune cells known as B cells. Claire Shannon-Lowe, a virologist at the University of Birmingham in Britain who studies the virus but was not involved in the research, said the virus does "a whole host of things" to the cells to keep them growing, including blocking normal cellular processes that would otherwise clear the virus and halt cancer development.

Uneven global burden

About three-quarters of infection-related cancers occurred in low- and middle-income countries, where access to vaccines, screening and treatment is often limited.

The share of cancers caused by infections appears lower than in some earlier estimates, which reached a high of 18% for 2002. But the authors cautioned that the figures cannot be reliably compared over time because data sources and quality have changed. The agency's previous analysis, for 2018, put the share at 13%.

Prevention possible for many cases

Researchers say the findings point to clear opportunities for prevention.

Some of the infections can be treated. H. pylori can be cleared with antibiotics, reducing the risk of stomach cancer, and treating HIV lowers the risk of related cancers.

Others can be prevented with vaccines, some of which were developed specifically with cancer prevention in mind.

"The hepatitis B virus vaccine was the first vaccine that was developed against cancer," Rumgay said.

The HPV vaccine, approved about 20 years ago, is designed to prevent cervical cancer. Rumgay said epidemiologists may begin to see its effects in future analyses as more vaccinated people reach the ages when cervical and other HPV-related cancers typically develop.

However, vaccines are not reaching everyone who could benefit. In the United States, hepatitis B vaccination rates among newborns have declined sharply over the past two years.

No vaccine yet for Epstein-Barr

For some infections, no vaccine exists. Rumgay said there is currently no effective vaccine or method of preventing Epstein-Barr virus infection, a gap the researchers wanted to highlight with their study.

Lawrence Young, an emeritus professor of molecular oncology at the University of Warwick in Britain who has studied the virus throughout his career, said it was historically difficult to interest pharmaceutical companies in vaccines against common, generally nonlethal viruses. Young was not involved in the research.

That has changed in part because of research suggesting Epstein-Barr virus may play a role in multiple sclerosis, an autoimmune disease. Drug companies have "all become very interested," Young said. Several vaccine candidates are now being studied, some in clinical trials.

Rumgay said more research into prevention is also needed for other cancer-causing infections, particularly the herpes virus associated with Kaposi sarcoma. She said the researchers hope the findings will spur further development in that area.

A call for action

The agency called for coordinated global action to reduce infection-related cancers through vaccination, infection control, screening and timely treatment.

Because many of these cancers stem from infections that can be prevented or treated, public health experts say they represent one of the most achievable targets for reducing the global cancer burden.