Five common infections drove 2.3 million cancer cases in 2024. Most were preventable.

About 2.3 million new cancer cases diagnosed worldwide in 2024 — roughly one in every eight — were caused not by genetics or lifestyle alone, but by infections that are largely treatable or preventable, according to a major new analysis published in The Lancet Oncology. The finding reframes a significant slice of the global cancer burden as a public health problem with known solutions, if those solutions can actually reach the people who need them.

Five pathogens were responsible for nearly all of those infection-linked cases. The most common was Helicobacter pylori — the stomach bacterium that statistically infects about one in every two people on Earth — which was linked to approximately 760,000 cancer cases, mostly gastric cancers. Human papillomavirus (HPV) was close behind at roughly 750,000 cases, predominantly cervical cancer. Hepatitis B virus (HBV) accounted for around 360,000 cases, Epstein-Barr virus (EBV) for around 260,000, and hepatitis C virus (HCV) for around 160,000.

We can intervene before it gets anywhere near cancer. We just need the politics and the finances and the buy-in from the public and the communication to get the programs implemented. Prevention works. It's an awareness-raising issue.— Gary Clifford, senior study author and epidemiologist, International Agency for Research on Cancer

For four of the five leading infectious causes — HPV, HBV, H. pylori, and HCV — effective prevention or treatment measures already exist. HPV and HBV each have vaccines. H. pylori can be detected through screening and cleared with antibiotics. HCV can be eliminated with antiviral treatments. EBV is the outlier: it infects an estimated 95 percent of adults worldwide, and no approved vaccine or reliable method to control its spread currently exists, though clinical trials for EBV vaccines are underway.

However, highly effective prevention measures already exist for four of the five leading infectious causes of cancer, as well as for HIV.— Harriet Rumgay, epidemiologist, International Agency for Research on Cancer and lead study author

The burden is not shared equally. Low- and middle-income countries accounted for 77 percent of all infection-attributable cancer cases, according to the study. Eastern Asia alone made up 42 percent of the global total, driven largely by H. pylori and HBV. Sub-Saharan Africa and southeastern Asia also carried disproportionate shares. The researchers attribute the disparity to both higher prevalence of the infections themselves and reduced access to vaccines, screening, and treatment.

The pattern holds within wealthy countries too. Veronika Fedirko, a professor of epidemiology at The University of Texas MD Anderson Cancer Center who was not involved in the study, pointed to a separate American Cancer Society analysis finding that in 2019, about 60,310 cancer cases among U.S. adults 30 and older — 3.4 percent of all cancers in that group — were attributable to seven infections, with HPV the largest contributor.

Even within the United States, the burden of infection-related cancer is not evenly distributed, and some populations have higher rates of infections such as hepatitis B, hepatitis C, HPV or H. pylori, while others have less access to vaccination, screening or treatment. And these differences can translate into disparities in cancer incidence many years later.— Veronika Fedirko, professor of epidemiology, The University of Texas MD Anderson Cancer Center

A critical caveat runs through all of this: having one of these infections does not mean a person will develop cancer. As Fedirko explained, cancer typically develops only in a small proportion of infected people, usually when an infection persists for many years and interacts with other factors — age, immune function, smoking, genetics, or other exposures. The infections raise risk; they do not guarantee an outcome.

EBV's inclusion in the analysis marks a significant update from the previous global estimate published in 2018. EBV was the first virus ever identified as a cancer-causing agent — discovered in connection with Burkitt lymphoma roughly 60 years ago — but the full scope of its cancer burden was not captured in earlier global analyses. The new study incorporated 16 additional infection-cancer pairs compared with the 2018 analysis, reflecting a substantially improved understanding of how these pathogens interact with human cells over time.

The American Cancer Society notes that scientists have known since the early 1900s that certain infections can cause cancer in animals, and that infections are now understood to raise cancer risk through several mechanisms — including causing chronic inflammation, suppressing the immune system, or directly altering the DNA of host cells. The agency lists viruses, bacteria, and parasites among the categories of infectious agents with established links to human cancer.

The study's authors are direct about where the bottleneck lies. The tools exist; the barriers are societal, financial, and political — and they tend to be highest in the places where infection-related cancer is most common. Getting more men vaccinated for HPV (vaccination programs have historically focused on women and girls) and expanding HBV vaccination coverage are identified as particularly high-impact opportunities. H. pylori presents a harder challenge: progress on developing an H. pylori vaccine has been slow, and highly effective therapies that minimize antibiotic resistance remain elusive.

Considering the overwhelming economic and social costs of cancer, investment in prevention is crucial.— Harriet Rumgay and colleagues

Why it matters — Infections behind more than 2 million cancers a year are largely preventable with existing vaccines and treatments — meaning a substantial share of the global cancer burden could be reduced if those tools reach the people who need them.

Reported by washingtonpost.com, sciencealert.com, theatlantavoice.com, cancer.org