Infections Drive 2.3 Million Cancer Cases a Year and Most Are Preventable

A Staggering Number With a Hopeful Twist

When most people think about cancer risk, they think about genetics, smoking, or diet. Infections rarely top the list. But a sweeping new study published September 28 in The Lancet Oncology makes the case that the world has been underestimating one of cancer's most common — and most preventable — causes.

Around 2.3 million new cancer cases globally were caused by viral, bacterial, and parasitic infections in 2024. That amounts to 12% of all new global cancer cases, according to the International Agency for Research on Cancer (IARC), the World Health Organization's cancer agency. Put simply: one in every eight cancers diagnosed last year didn't have to happen.

The Culprits Behind the Numbers

Five pathogens were responsible for the majority of infection-linked cancers: Helicobacter pylori (760,000 cases), human papillomavirus or HPV (750,000 cases), hepatitis B virus or HBV (360,000 cases), Epstein-Barr virus or EBV (260,000 cases), and hepatitis C virus or HCV (160,000 cases). These infections were linked to over 20 cancer types, including cervical, stomach, liver, and lymphatic cancers.

The largest single contributor was H. pylori, the bacterium that can increase the risk of stomach cancer, accounting for 760,000 cases predominantly in eastern Asia. HPV, which causes 100% of cervical cancer cases and also anal, vulvar, vaginal, penile, and some head and neck cancers, accounted for nearly 750,000 new cases globally, with high rates in sub-Saharan Africa. One of the more surprising findings involved the Epstein-Barr virus — a pathogen familiar to many as the cause of mono. Its role proved larger than expected due to new evidence showing it also has a causal role in gastric cancer, beyond its previously known links to nasopharyngeal cancer and lymphoma.

Researchers explained that many of these infections "hijack the cellular machinery" that controls the normal cell cycle to help their own replication — in doing so, they disable the mechanisms that would normally repair mutated genes or instruct damaged cells to die, while chronic inflammation and repeated tissue damage further increase the risk.

A Burden That Falls Unevenly

"Despite progress in vaccination and screening, infection-related cancers remain a major global challenge, with the burden falling disproportionately on populations in low- and middle-income countries," said Harriet Rumgay, a scientist in the Cancer Surveillance Branch at IARC and a co-author of the study. In high-income countries, infection-related cancers represent a small fraction of the total disease burden, largely mitigated by widespread childhood vaccination programs, blood supply screening, and access to antiviral medications.

"In some settings, prevention programs are also affected by financial constraints, insufficient political commitment, and inequitable access to care," the researchers noted. The gap between what is scientifically possible and what is actually delivered to the world's most vulnerable populations remains wide — and costly in human lives.

The Tools Already Exist

Lead author Harriet Rumgay said that "while this burden is enormous, it is also largely preventable," pointing out that effective tools and public health strategies already exist to prevent many infection-related cancers, including vaccination, screening, testing, and treatment programs.

IARC scientists said that policymakers and health systems should prioritize scaling up proven interventions, such as vaccination against HPV and HBV; testing and treatment for H. pylori, HBV, HCV, and HIV; measures to prevent transmission like safe injection practices and access to condoms; and cervical cancer screening. The authors also recommend measures spanning primary prevention, screening, treatment, research, and policy — from scaling up existing vaccines and developing new ones to introducing parasite-specific control measures and expanding testing.

The research builds on three decades of work by the study's authors, who have examined infection-linked cancers in 1990, 2002, 2008, 2012, and 2018, though the authors cautioned that data quality and sources have evolved, making direct comparisons across years unreliable. What is clear is the direction forward: "Large reductions in cancer burden are achievable with existing interventions, and ensuring equitable access should be a global priority."