One in Eight Worldwide Cancer Cases Linked to Infections, WHO Study Finds

An estimated 12 percent of all new cancer cases worldwide in 2024, translating to approximately 2.3 million diagnoses, were likely caused by infections, according to comprehensive new research published in The Lancet Oncology. The study, conducted by the International Agency for Research on Cancer (IARC) under the World Health Organization, provides an updated evaluation of how viral, bacterial, and parasitic pathogens drive oncogenesis across more than 20 distinct cancer types.

According to International Agency for Research on Cancer, for Regional Infection-Attributable Cancer Fractions, Infection-linked cancers represent over 20-25% of cancer diagnoses in low-HDI countries compared to just 4-5% in high-income regions, underpinning the 75% LMIC global burden. According to International Agency for Research on Cancer (IARC), iARC published its 2024 global cancer assessment in The Lancet Oncology on September 29, 2026, finding that 2.3 million new cancer cases (12% globally) were caused by infectious agents.

Five primary pathogens accounted for the vast majority of these infection-linked cases, led by Helicobacter pylori and human papillomavirus at four percent each. Hepatitis B contributed two percent, the Epstein-Barr virus accounted for one percent, and hepatitis C was responsible for under one percent of the total global burden. Researchers noted that the analysis incorporates newly established infection-cancer associations, such as emerging evidence linking the Epstein-Barr virus to gastric cancer, as well as broader tracking of agents like HIV and Merkel cell polyomavirus.

According to World Health Organization, infectious agents cause 11.8% of global cancers, ranking behind tobacco (20-22%) but exceeding alcohol consumption (4-5%) and obesity (5-6%) in preventable cancer burden. According to International Agency for Research on Cancer (IARC), the 2024 IARC study updated its methodology by incorporating HIV co-carcinogenesis, Merkel cell polyomavirus, and EBV-linked gastric cancer, precluding direct comparisons with older assessments.

Pathogenic Mechanisms Driving Cellular Transformation

Infections induce malignancy through sharply contrasting biological pathways depending on the organism involved. Viral pathogens act directly or indirectly by altering host cell genetics, actively driving uncontrolled cellular proliferation. Viruses achieve this via three established mechanisms: inactivating tumor suppressor proteins such as TP53 and RB that normally force damaged cells to self-destruct or halt division, integrating viral DNA directly into the host genome to disrupt cell-cycle regulation, or carrying foreign oncogenes acquired from other organisms.

Bacteria and parasites employ more indirect pathways centred on chronic tissue stress and prolonged inflammation. Long-term immune responses to pathogens such as Helicobacter pylori or the liver fluke Opisthorchis viverrini generate continuous cellular damage. As surrounding tissues attempt rapid repair, frequent replication errors and DNA damage accumulate, ultimately placing affected cells on the trajectory toward malignant transformation.

Global Disparities and Preventative Interventions

The findings underscore that a substantial share of global cancer diagnoses remain entirely preventable through targeted public health measures. Investigators revealed that roughly 75 percent of all infection-linked cancers occurred in low- and middle-income countries, highlighting persistent global inequities in healthcare access, diagnostic screening, and preventative therapies.

Gary Clifford, senior author of the study and an epidemiologist at the IARC, emphasized that these risk factors are highly actionable. Experts pointed to established prophylactic interventions, including antibiotics to eradicate H. pylori, screenings and treatments for hepatitis C, hepatitis B vaccinations, and widespread administration of the human papillomavirus vaccine, which has proven effective in reducing cervical and throat cancer rates over the past two decades.