Some infections do not merely cause a temporary illness: years later, they can also promote the development of cancer.
A new global analysis estimates that 2.3 million cancers diagnosed in 2024 were attributable to infections. This represents around 12% of new cases, or nearly one in eight cancers. Researchers at the International Agency for Research on Cancer used global incidence data to measure the share associated with twelve infectious agents recognized as carcinogenic.
Human papillomavirus observed under an electron microscope and colorized.
Credit: NIAID
To understand this link, it is important to distinguish between infection and cancer. An infection does not immediately transform a healthy cell into a cancer cell. However, some microbes can remain in the body for a long time. This lasting presence can sustain inflammation or disrupt cell function, gradually increasing the risk of a tumor developing.
Two agents play a particularly important role. The bacterium Helicobacter pylori, which can live in the stomach for years, is primarily associated with gastric cancer. Human papillomavirus, or HPV, is responsible for the vast majority of cervical cancers. Together, these two infections account for more than 1.5 million estimated cases.
Hepatitis B and C viruses are also among the leading infectious causes of cancer. A persistent infection can progressively damage the liver and promote cancer in that organ. Epstein-Barr virus is associated with several cancers, including certain lymphomas and nasopharyngeal cancers. Recent studies also link it to some stomach cancers.
The risk depends on the microbe, the duration of the infection and many other factors. The study calculates, at the population level, how many cancers probably would not have occurred in the absence of these infections.
This distinction has a practical consequence: some of these cancers can be prevented before a tumor even forms. Vaccines are available against HPV and hepatitis B. Other infections can be detected and then treated, notably Helicobacter pylori and hepatitis C. Cervical screening can also identify lesions before they transform into cancer.
The situation varies greatly across regions of the world. Exposure to infections, vaccination, access to screening and access to treatment are not the same everywhere. The burden of infection-related cancers is therefore significantly higher in some populations, particularly in several low- and middle-income countries.
The researchers also expanded their analysis compared with previous estimates. They incorporated new associations between infections and cancers, as well as additional agents, including HIV and Merkel cell polyomavirus. These data can now be used to target vaccination, screening and treatment campaigns more precisely.