Cancer is usually linked to factors such as smoking, alcohol use, obesity, pollution, family history and ageing. However, a new study has now highlighted another important risk factor, and that is infections. According to a study published in The Lancet Oncology, an estimated 2.3 million new cancer cases worldwide in 2024, or about 12% of all cancer cases, were linked to infections. In other words, around one in every eight cancers diagnosed globally that year was linked to an infection.

The study by researchers from the International Agency for Research on Cancer (IARC) looked at cancer data from 2024 and included infectious agents known to cause cancer. Five infections accounted for almost all infection-related cancer cases. These included Helicobacter pylori (H. pylori), human papillomavirus (HPV), hepatitis B virus (HBV), Epstein-Barr virus (EBV) and hepatitis C virus (HCV). The findings are important because several of these infections can be prevented, detected or treated, which can eventually reduce the risk of some cancers.

Which Infections Are Linked To Cancer?

The study assessed 12 infectious agents which are known to have cancer-causing effects in humans. However, five infections were responsible for nearly all of the 2.3 million infection-related cancer cases in 2024.

  • H. pylori: This stomach bacterium was linked to around 760,000 cancer cases, making it the largest contributor. It is mainly associated with stomach cancer.
  • HPV: The virus was linked to about 750,000 cases. Persistent infection with high-risk HPV types is the main cause of cervical cancer and is also associated with anal, vulvar, vaginal, penile and some head and neck cancers.
  • Hepatitis B virus: HBV was associated with around 360,000 cancer cases, mainly liver cancer.
  • Epstein-Barr virus: EBV was linked to approximately 260,000 cases, including some stomach cancers, nasopharyngeal cancers and certain lymphomas.
  • Hepatitis C virus: HCV was associated with about 160,000 cases, most of them involving liver cancer.

The researchers also included newer evidence linking EBV with stomach cancer, along with additional cancer types and infectious agents in their updated analysis.

Dr Harriet Rumgay, a scientist in the Cancer Surveillance Branch at IARC and co-author of the article, said, "The findings underscore the major role that infection control can play in reducing the global cancer burden. 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."

How Can Infections Cause Cancer?

Not every person who develops one of these infections will develop cancer. Cancer risk depends on factors including the type of infection, how long it persists, the person's immune response and other risk factors.

Some infections can cause long-term inflammation or damage to cells and tissues. Over many years, persistent infection can contribute to changes in cells that may eventually become cancerous. For example, chronic HBV and HCV infections can damage the liver and increase the risk of liver cancer. Persistent infection with high-risk HPV types can cause changes in cervical cells that may progress to cervical cancer if they are not detected and treated. H. pylori can cause long-term inflammation in the stomach and is strongly linked to stomach cancer.

Low- And Middle-Income Countries Carry A Large Burden

The burden of infection-related cancers is not distributed equally around the world. According to the IARC analysis, about 77% of these cancers occurred in low- and middle-income countries. This difference is linked partly to variations in infection rates, vaccination coverage, cancer screening, access to testing and availability of treatment.

This means that improving access to basic preventive healthcare could have an important effect on cancer prevention in areas carrying a high infection-related burden.

Can Infection-Related Cancers Be Prevented?

Some infection-related cancers are potentially preventable through vaccination, screening, testing and treatment.

The HPV vaccine can protect against the HPV types responsible for most cervical cancers and several other HPV-related cancers. Screening can also identify cervical changes before they develop into invasive cancer.

The hepatitis B vaccine can help prevent chronic HBV infection and, in turn, reduce the risk of liver cancer. Hepatitis C does not currently have a vaccine, but effective antiviral treatment can cure most HCV infections.

The study says that infection control is also an important part of reducing the cancer burden. The researchers highlight the role of vaccination, screening and treatment, which can help prevent cancers linked to infections.

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