Major study links infections to 1 in 8 new cancer cases worldwide

A new analysis from the International Agency for Research on Cancer (IARC) found that about one in eight newly diagnosed cancer cases worldwide — 2.3 million cases — were associated with infections.

The study identified 12 infections linked to human cancers, including Helicobacter pylori (H. pylori), human papillomavirus (HPV), hepatitis B virus (HBV), hepatitis C virus (HCV), Epstein–Barr virus (EBV), Kaposi sarcoma-associated herpesvirus, Schistosoma haematobium, HTLV-1, Opisthorchis viverrini, Clonorchis sinensis, Merkel cell polyomavirus and HIV.

Five of those infections accounted for nearly all of the global cases.

• H. pylori: about 760,000 cases

• HPV: about 750,000 cases

• HBV: about 360,000 cases

• EBV: about 260,000 cases

• HCV: about 160,000 cases

“The findings underscore the major role that infection control can play in reducing the global cancer burden,” said study co-author Dr. Harriet Rumgay, a scientist in the Cancer Surveillance Branch at IARC, in a press release.

“Despite progress in vaccination and screening, infection-related cancers remain a major global challenge, with the burden falling disproportionately on populations in low- and middle-income countries.”

The researchers said many of these cancers might have been prevented through vaccination, treatment or screening.

Conducted in France, the study analyzed cancer data from 2024, and the findings were published in The Lancet Oncology.

The researchers also noted several limitations.

Because the analysis used population-level estimates rather than tracking individual patients over time, its accuracy depended on the quality of cancer data available in each country.

It also covered only infections already proven to cause cancer, which means the overall impact could be larger than reported.

“We know that there are certain infections that we are exposed to over our lifetime that may result in an increased risk of certain cancers,” Dr. Joshua Cohen, medical director of the Gynecologic Cancer Program of City of Hope Orange County in Irvine, California, said.

“However, most cancers are not caused by infection.”

According to Cohen, who was not involved in the study, HPV is one of the most common causes of cancers of the rectum, vagina or cervix, as well as the oropharynx, or the back of the throat.

“Eighty percent of the population has been exposed to certain types of HPV strains,” he said. “About 40,000 people in the U.S. are diagnosed with these cancers each year.”

For most people exposed to HPV, the body clears the virus on its own, Cohen said.

“We don’t know why some patients’ immune systems allow them to clear the HPV infection and some don’t.”

He added that another common cancer, though less common in the U.S., is gastric cancer, which is linked to H. pylori, a stomach infection.

“We don’t screen everybody for H. pylori in the U.S. — it’s more common in other parts of the world, like Southeast Asia.”

People with peptic ulcer disease or significant epigastric pain should speak with a gastroenterologist about testing and treatment for H. pylori, he advised.

Cohen said there are steps people can take to reduce the risk of infection-related cancers.

“As a patient, the most important thing is to think about your health, what you can do to prevent yourself from developing these infections or your family,” he said.

“And if you do have one of these infections, what can you do to reduce your risk of developing a subsequent cancer?”

He emphasized that an HPV vaccine is available and can help prevent many of the cancers tied to the virus.

“If you’re under the age of 45 and you’ve not had an HPV vaccination, there is various good safety data that you should get vaccinated,” he said. “That will cover, at least in the U.S., most risks regarding oropharyngeal cancers, vaginal cancers, cervical cancers, penile cancers and anal cancers.”

He also stressed that being infected with one of the listed pathogens does not mean a person will develop cancer.

“The vast majority of patients who have an HPV infection or H. pylori, or even hepatitis B or C, are not going to develop cancer,” he said.

Still, because these infections have been linked to certain cancers, treatment matters.

Symptoms such as epigastric pain, acid reflux, abnormal vaginal bleeding or pain with swallowing may point to medical conditions associated with certain infections or cancers, he warned.

“There are steps we can take as doctors to keep you safe and hopefully reduce the risk of developing cancer for those that have had an infection,” Cohen added.