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A new global analysis has put a number on something researchers have long suspected: a significant share of the world's cancers begin with an infection.
The study, from the World Health Organization's cancer agency (the International Agency for Research on Cancer), published in The Lancet Oncology, estimates that about 2.3 million new cancer cases worldwide in 2024 — roughly 1 in 8 of all cases — were linked to infections with viruses, bacteria, or parasites. The researchers say many of these could have been prevented with tools that already exist, such as vaccines, screening, and treatment of the infections themselves.
The Five Infections Behind Most of These Cases
The analysis looked at 12 infectious agents classified as definite carcinogens. Just five of them accounted for more than 2.2 million of the estimated 2.3 million infection-linked cases:
Helicobacter pylori (H. pylori) — about 760,000 cases, mostly stomach cancers.
Human papillomavirus (HPV) — about 750,000 cases, led by cervical cancer but also including some anal and head-and-neck cancers. All cervical cancer cases in the analysis were attributed to HPV.
Hepatitis B — about 360,000 cases, mostly liver cancers.
Epstein-Barr virus (EBV) — about 260,000 cases, including nasopharyngeal cancer, Hodgkin's lymphoma, and some gastric cancers.
Hepatitis C — about 160,000 cases, mostly liver cancers.
Together, H. pylori and HPV alone were behind roughly 1.5 million cases in 2024.
How Can an Infection Lead to Cancer?
The idea is not that a single infection immediately causes cancer. Rather, certain long-term infections can quietly damage cells over many years, and in some people that slow, cumulative damage eventually tips into cancer. This is also why prevention works on a long timeline: treating or vaccinating against the infection can stop the process long before it reaches that point. As the study's senior author put it, "we can intervene before it gets anywhere near cancer."
The Encouraging Part: Much of This Is Preventable
Unlike many cancer risk factors, these infections have known, existing countermeasures:
Vaccines — HPV and hepatitis B vaccines are among the most effective tools we have, and they work best when given before exposure.
Testing and treatment — H. pylori can be detected with simple tests and treated with antibiotics; chronic hepatitis B and C have antiviral treatments that lower liver-cancer risk.
Screening — Cervical screening catches HPV-related changes early, when they are most treatable.
The researchers note that the burden falls heaviest where these prevention tools reach the fewest people — which makes awareness itself part of the solution.
Frequently Asked Questions
Q: If I get one of these infections, will I get cancer?
No. Most infections never lead to cancer — the study estimates population-level shares, not individual risk. Cancer develops in some people after years of persistent infection. If you have symptoms or concerns, talk to a clinician rather than trying to self-assess your risk.
Q: What should I ask my doctor about?
HPV vaccination, hepatitis B vaccination, and testing or treatment for H. pylori if you have persistent stomach symptoms are the topics researchers highlight most. But which of these apply to you depends on your age, history, and local health guidance — a clinician can advise on what fits your situation.
Q: Do the usual healthy habits still matter?
Yes. Infection prevention adds to established steps — not smoking, a balanced diet, regular physical activity, and recommended cancer screenings — rather than replacing them.
The Bottom Line
About 1 in 8 cancers in 2024 had a preventable beginning: an infection we already know how to stop. Vaccines, screening, and straightforward treatment exist for the biggest culprits. The gap is not knowledge — it is making sure those tools reach everyone.
Medical Disclaimer: This post is for general informational purposes only and is not medical advice. Talk to your doctor or another qualified health professional about any health question. See the site's Disclaimer page for more.
Source: International Agency for Research on Cancer analysis, published in The Lancet Oncology (2026), based on 2024 global cancer data.
The study, from the World Health Organization's cancer agency (the International Agency for Research on Cancer), published in The Lancet Oncology, estimates that about 2.3 million new cancer cases worldwide in 2024 — roughly 1 in 8 of all cases — were linked to infections with viruses, bacteria, or parasites. The researchers say many of these could have been prevented with tools that already exist, such as vaccines, screening, and treatment of the infections themselves.
The Five Infections Behind Most of These Cases
The analysis looked at 12 infectious agents classified as definite carcinogens. Just five of them accounted for more than 2.2 million of the estimated 2.3 million infection-linked cases:
Helicobacter pylori (H. pylori) — about 760,000 cases, mostly stomach cancers.
Human papillomavirus (HPV) — about 750,000 cases, led by cervical cancer but also including some anal and head-and-neck cancers. All cervical cancer cases in the analysis were attributed to HPV.
Hepatitis B — about 360,000 cases, mostly liver cancers.
Epstein-Barr virus (EBV) — about 260,000 cases, including nasopharyngeal cancer, Hodgkin's lymphoma, and some gastric cancers.
Hepatitis C — about 160,000 cases, mostly liver cancers.
Together, H. pylori and HPV alone were behind roughly 1.5 million cases in 2024.
How Can an Infection Lead to Cancer?
The idea is not that a single infection immediately causes cancer. Rather, certain long-term infections can quietly damage cells over many years, and in some people that slow, cumulative damage eventually tips into cancer. This is also why prevention works on a long timeline: treating or vaccinating against the infection can stop the process long before it reaches that point. As the study's senior author put it, "we can intervene before it gets anywhere near cancer."
The Encouraging Part: Much of This Is Preventable
Unlike many cancer risk factors, these infections have known, existing countermeasures:
Vaccines — HPV and hepatitis B vaccines are among the most effective tools we have, and they work best when given before exposure.
Testing and treatment — H. pylori can be detected with simple tests and treated with antibiotics; chronic hepatitis B and C have antiviral treatments that lower liver-cancer risk.
Screening — Cervical screening catches HPV-related changes early, when they are most treatable.
The researchers note that the burden falls heaviest where these prevention tools reach the fewest people — which makes awareness itself part of the solution.
Frequently Asked Questions
Q: If I get one of these infections, will I get cancer?
No. Most infections never lead to cancer — the study estimates population-level shares, not individual risk. Cancer develops in some people after years of persistent infection. If you have symptoms or concerns, talk to a clinician rather than trying to self-assess your risk.
Q: What should I ask my doctor about?
HPV vaccination, hepatitis B vaccination, and testing or treatment for H. pylori if you have persistent stomach symptoms are the topics researchers highlight most. But which of these apply to you depends on your age, history, and local health guidance — a clinician can advise on what fits your situation.
Q: Do the usual healthy habits still matter?
Yes. Infection prevention adds to established steps — not smoking, a balanced diet, regular physical activity, and recommended cancer screenings — rather than replacing them.
The Bottom Line
About 1 in 8 cancers in 2024 had a preventable beginning: an infection we already know how to stop. Vaccines, screening, and straightforward treatment exist for the biggest culprits. The gap is not knowledge — it is making sure those tools reach everyone.
Medical Disclaimer: This post is for general informational purposes only and is not medical advice. Talk to your doctor or another qualified health professional about any health question. See the site's Disclaimer page for more.
Source: International Agency for Research on Cancer analysis, published in The Lancet Oncology (2026), based on 2024 global cancer data.
