Most of us think of cancer as something that strikes out of nowhere.
We watch our diet, we try to sleep, we move more. The idea that an infection could be behind the diagnosis rarely crosses our minds.
But a new worldwide analysis in The Lancet Oncology estimates that 2.3 million cancer cases in 2024, roughly 1 in every 8 diagnoses, were caused by infections.
The authors stress that many of these cases could be headed off with vaccines, antibiotics and antivirals that are already available today.
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The analysis comes from the World Health Organization's International Agency for Research on Cancer (IARC). It is the largest estimate of infection-attributable cancers to date and covered bacteria, viruses and other agents known to raise cancer risk.
Five infections account for almost all these cancers
The researchers found five pathogens behind the vast majority of infection-related diagnoses in 2024:
- Helicobacter pylori, a stomach bacterium: about 760,000 cases, mostly stomach cancer
- Human papillomavirus (HPV): about 750,000 cases, including cervical, anal and some head and neck cancers
- Hepatitis B virus: about 360,000 cases, mainly liver cancer
- Epstein-Barr virus (EBV): about 260,000 cases, linked to lymphomas and some stomach and nasopharyngeal cancers
- Hepatitis C virus: about 160,000 cases, mostly liver cancer
According to the International Agency for Research on Cancer, more than three-quarters of these cancers occurred in low- and middle-income countries.
Eastern Asia alone accounted for about 42 percent of the global total.
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HPV and hepatitis B are vaccine-preventable
The HPV vaccine blocks the strains that cause nearly all cervical cancers, along with several cancers of the mouth, throat and anal area.
The hepatitis B vaccine prevents the virus that is a major cause of liver cancer worldwide.
Both vaccines have been available for years, but coverage is still uneven across age groups and regions.
Hepatitis C, once a lifelong infection, is now curable for most people with a short course of direct-acting antiviral pills. A one-time blood test can tell you whether you carry the virus.
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H. pylori can be tested and treated
Helicobacter pylori, the single biggest cause of infection-related cancers in the study, is a bacterium that lives in the stomach lining.
The World Health Organization estimates it is present in roughly half of all people worldwide, yet most carriers have no idea.
A simple breath test or stool test can detect it. A short course of antibiotics combined with an acid-reducing medication clears the infection in most people.
If you have ongoing stomach pain, repeated indigestion or a family history of stomach cancer, talk with your doctor about whether H. pylori testing makes sense for you.
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What this means for the reader
Not every cancer in the study can be prevented today, but a large share can.
The HPV vaccine, the hepatitis B vaccine, hepatitis C antivirals and H. pylori testing are all available through primary care.
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This article is made and published by Ida-Marie Palm Varbæk, who may have used AI in the preparation.