Infections such as HPV and H. pylori account for millions of cancer cases worldwide

An analysis by the International Agency for Research on Cancer estimates that 2.3 million new cancer cases in 2024 – roughly one in eight worldwide – were associated with infectious agents. The study identified 12 infections that cause cancer, but five accounted for the majority of cases: Helicobacter pylori (about 760,000 cases), human papillomavirus (around 750,000), hepatitis B virus (≈ 360,000), Epstein–Barr virus (≈ 260,000) and hepatitis C virus (≈ 160,000).

"The findings underscore the major role that infection control can play in reducing the global cancer burden," said Dr. Harriet Rumgay, a scientist in IARC's Cancer Surveillance Branch.

The researchers noted that many of these cancers could be prevented through existing vaccines, treatments or screening programs. The analysis, based on population-level cancer data for 2024, was published in The Lancet Oncology.

Limitations include reliance on aggregate data rather than individual patient follow-up and the exclusion of infections not yet proven to cause cancer, which may lead to an underestimate of the true impact.

Experts highlighted that while HPV infection is common – about 80 % of people are exposed to high-risk strains – most infections are cleared by the immune system and do not progress to cancer. Similarly, H. pylori infection is more prevalent in regions such as Southeast Asia, and screening is recommended for individuals with peptic ulcer disease or persistent upper-abdominal pain.

"If you’re under the age of 45 and you haven’t had an HPV vaccination, there is good safety data supporting vaccination to reduce the risk of several HPV-related cancers," said Dr. Joshua Cohen, medical director of the Gynecologic Cancer Program at City of Hope.

Both experts emphasized that infection does not guarantee cancer development, but timely diagnosis and treatment of the infections can lower risk.