1 in 8 Cancers Are Infection-Linked Cancers, WHO Study Finds

Roughly one in eight cancers diagnosed worldwide in 2024 can likely be traced to an infection, according to a sweeping analysis by World Health Organization researchers published today in The Lancet Oncology. The study ties about 2.3 million new cases that year to infection-linked cancers, most of them driven by just five pathogens. It is the latest in a line of global estimates the same research community has produced every few years for about three decades, with the previous edition published in 2018, and the authors say the real point is not the trend line. It is the takeaway: a large share of the world's cancer burden is, in principle, preventable.

Five pathogens behind most infection-linked cancers

Five bugs cause almost all infection-linked cancers. Helicobacter pylori, a bacterium best known for causing stomach ulcers, was tied to some 760,000 cases, roughly four percent of the world's cancer total. Human papillomavirus, or HPV, one of the most common sexually transmitted infections in the world, followed with around 750,000 cases. Hepatitis B accounted for about 360,000, Epstein-Barr virus for some 260,000 and hepatitis C for around 160,000. Together these infections can cause more than 20 types of cancer, including stomach, liver, blood and cervical cancers, the researchers report.

The biology is well worked out. A virus can push a host cell toward cancer in three main ways, the study authors note: by switching off the cell's self-destruct or stop-dividing controls, proteins known as TP53 and RB, by splicing viral DNA into the host genome where it can scramble those same controls, or by carrying a cancer-causing gene of its own. Bacteria and parasites work more indirectly. Long-running infections like H. pylori or the liver fluke Opisthorchis viverrini keep tissue inflamed for years, and chronic inflammation can damage tissue and introduce the DNA mistakes that start a tumor.

H. pylori itself is remarkably widespread. The UK's National Health Service estimates that around 40 percent of people in Britain have been exposed to the bacterium, with about one in ten developing symptoms, according to reporting by The Sun. Most carriers never know they have it. That gap between exposure and illness is part of why the researchers argue that treating infections early, including H. pylori, HIV and hepatitis B and C, is one of the most direct ways to cut the toll of infection-linked cancers.

Prevention works, and sexual health is part of it

The study's authors point to a short list of defenses: vaccination, condoms and disease screening, all familiar tools from sexual health campaigns. HPV is the clearest example of what those defenses can do. In Australia, where adolescents have been offered the HPV vaccine since 2007, infections have dropped to roughly a tenth of their former level among eligible groups, and the country is on track to effectively eliminate cervical cancer by 2035. The warning sits beside the win: uptake among 15-year-olds has slipped from roughly 86 percent in 2020 to about 80 percent in 2024, far short of the WHO goal of vaccinating 90 percent of 15-year-old girls by 2030.

The burden falls hardest where resources are thinnest

About three-quarters of infection-linked cancers were found in low- and middle-income countries, where vaccines, screening and treatment remain hardest to reach. The researchers caution against reading the headline share as a trend: earlier estimates from the same group ran as high as 18 percent back in 2002, but data sources and quality have changed too much for a clean comparison. The argument underneath is simpler. Infection-linked cancers represent one of the clearest prevention opportunities in global health, and controlling the infections behind them is one of the most direct ways to bring cancer rates down.

For younger readers, the ones weighing vaccine and screening decisions right now, the message is personal. HPV spreads through sexual contact and is so common that most sexually active people encounter it. Vaccination before exposure, condoms and regular screening are the tools that keep it from becoming cancer years later. The researchers describe the link between infections and cancer as indisputable, which means a meaningful share of future infection-linked cancers never has to happen.