Everyday Infections Are Behind 1 in 8 Cancer Cases Worldwide — and Many Are Preventable

A Hidden Driver of Cancer

Most people think of cancer as a product of bad genes, smoking, or environmental exposure. But a major new study is reshining a spotlight on a factor that often flies under the radar: common infections. A report by the World Health Organization's International Agency for Research on Cancer (IARC), published in The Lancet Oncology, found that 12 infections were linked to approximately 12% of new cancer cases worldwide in 2024. That translates to a staggering toll — about 2.3 million new cancer cases worldwide in 2024 were caused by infections, representing 1 in 8 of all new cancer cases globally.

The findings underscore how some common viruses and bacteria can raise cancer risk, even years after the initial infection. And while that sounds alarming, researchers are emphasizing a more hopeful message: a sizable share of the cancer burden around the world is preventable with tools we already have, including vaccines and other preventive measures. As cancer epidemiologist Gary Clifford, one of the study's authors, put it: "We have very actionable targets. We have very many tools against these viruses already."

The Five Biggest Offenders

Researchers examined 12 infectious agents known to cause cancer. Five accounted for almost all infection-related cases: Helicobacter pylori (H. pylori), human papillomavirus (HPV), hepatitis B virus (HBV), Epstein-Barr virus (EBV), and hepatitis C virus (HCV). These aren't obscure pathogens — they circulate widely, and many people carry them without knowing it.

H. pylori was the biggest contributor, accounting for an estimated 760,000 cancer cases in 2024. Chronic H. pylori infection can cause inflammation and changes in the stomach lining that increase the risk of stomach cancer and a rare type of lymphoma called gastric MALT lymphoma. HPV was close behind, responsible for an estimated 750,000 cancer cases worldwide in 2024. Meanwhile, Epstein-Barr virus (EBV) infects more than 90 percent of the world's population and was linked to around 1 percent of new cases, including some lymphomas, stomach cancer, and nasopharyngeal cancer. An estimated 360,000 cancer cases were attributed to hepatitis B virus and 160,000 to hepatitis C.

What You Can Do to Lower Your Risk

The good news is that for most of these infections, prevention and treatment options already exist. Highly effective prevention measures already exist for four of the five leading infectious causes of cancer — HPV and hepatitis B, for which vaccines are available, as well as H. pylori and hepatitis C, for which testing and treatments are available. The HPV vaccine, first introduced in the U.S. in 2006, can prevent six different cancers, including cervical cancer, throat cancer, and anal cancer.

H. pylori can be treated with medication, and studies show that eradicating the infection can reduce the risk of stomach cancer. People diagnosed with H. pylori should take the prescribed treatment as directed and follow up with their healthcare provider to make sure the infection has cleared. People can also be screened and treated for hepatitis C and vaccinated against hepatitis B, both of which can cause liver cancer. , although certain infections can raise a person's risk of some types of cancer, most people with these infections never develop cancer, and the risk is also influenced by other factors.

A Call for Broader Action

Scientifically proven, but often underused, approaches include HPV and HBV vaccination; testing and treatment of HIV, H. pylori, HBV, and HCV; safe injection practices; access to condoms and pre-exposure prophylaxis to prevent HIV transmission; and screening of precancerous lesions for HPV-driven cervical and anal cancer. Key challenges include limited access to and uptake of vaccination, screening, and diagnosis and treatment of infections, as well as social stigma related to infections such as HPV and HIV. In some settings, prevention programs are also affected by financial constraints, insufficient political commitment, and inequitable access to care.

One area where science still has work to do: EBV. The findings highlight where future investments in new prevention tools could have the greatest impact, particularly for infections such as EBV, for which effective vaccines are not yet available. Investment in new prevention tools, including EBV vaccines, should be a priority, the researchers said. For now, the most powerful takeaway from this research is a reminder that cancer prevention isn't only about what we eat or whether we smoke — sometimes, it starts with a doctor's visit, a vaccine, or a simple test.