Here is a finding that should reframe how you think about cancer: roughly one case in eight is, at bottom, an infectious-disease problem. In an analysis published Sept. 28 in The Lancet Oncology, researchers tallied up the global damage done by 12 cancer-causing pathogens — viruses, one bacterium and parasites — and estimated that infections were behind about 2.3 million of the new cancer cases diagnosed in 2024, or about 12% of the total. The total came from the Global Cancer Observatory’s GLOBOCAN database, which pools cancer registries to estimate that about 20 million new cases were diagnosed that year; the researchers then layered on published data about how often specific infections show up in specific cancers to work out what share each germ was responsible for.
The takeaway, as Dr. Prashant Mathur, director of India’s National Centre for Disease Informatics and Research, told Live Science in an email, is that a large fraction of cancer could be avoided by preventing the underlying infections. Mathur, who was not involved in the study, put it in the context of everything else we already know how to fix: “When combined with other risk factors such as tobacco use, alcohol consumption, appropriate diet, physical activity, and environmental pollution, it is estimated that about 50 to 60 percent of all cancers in India are avoidable,” he said, adding that past studies suggest similar figures hold globally.
Sure. But here is the part that matters if you like your prevention cheap and concentrated: just four of the 12 pathogens caused roughly 92% of the infection-driven cancers.
The leaderboard, per the study: Helicobacter pylori, a bacterium that colonizes the gastrointestinal tract, accounted for 760,000 cases, primarily stomach cancers. Human papillomavirus accounted for 750,000 — cervical cancers mostly, plus penile, throat and mouth cancers. Hepatitis B, which attacks the liver, drove 360,000. And Epstein-Barr virus, the germ behind mononucleosis, drove 260,000, through its links to throat cancers, certain lymphomas and some stomach cancers. Add those up and you get 2.13 million cases out of 2.3 million — about 92.6%, for a market in human misery with a remarkable degree of concentration. Fifth place, hepatitis C at 160,000 cases according to the study’s abstract, barely moves the needle. Geographically the burden clusters too: eastern Asia alone accounted for 990,000 cases, 42% of the global total, according to the International Agency for Research on Cancer.
The vaccine that already works
Now for the strange economics of the thing. You might assume that preventing cancer requires some magnificent future breakthrough. For two of the top four causes, the breakthrough already happened and is sitting in a vial. There is a highly effective vaccine against HPV. There is a highly effective vaccine against hepatitis B, which health officials recommend giving children as soon as possible after birth. These are, functionally, cancer vaccines — among the only ones humanity has — and the problem is not inventing them but shipping them.
The shipping is going badly. The World Health Organization reports that in 2024 just 31% of eligible adolescent girls worldwide received even one dose of the HPV vaccine, against a target of 90%. Meanwhile, in the places that did ship, the results are about as close to a controlled experiment as public health gets. “We have now achieved the critically important milestone of cervical cancer starting to disappear in countries that quickly achieved vaccination rates of over 80 percent,” Dr. Rebecca Perkins, an obstetrician-gynecologist at Tufts University School of Medicine who was not involved in the study, told Live Science. “Research from Australia, England, and Finland have shown zero cases of HPV-related cancers or deaths in young adults who received vaccination by age 13.”
Zero cases. The catch is that those successes are concentrated in wealthy countries, while the Lancet study found that low- and middle-income countries carry 77% of the global infection-driven cancer burden — including about 81% of HPV-linked cancers. Which is to say the disease clusters exactly where the vaccine doesn’t. Perkins noted that shifting from the standard two-dose series to a single dose of the same vaccines — an approach backed by recent trials — could make mass campaigns feasible by cutting costs and eliminating the need to track patients down for a second visit. Halve the doses, roughly halve the cost, delete the follow-up problem: it is less a medical innovation than a logistics one, which is probably why it might actually work.
In the U.S., coverage is a patchwork, with some states vaccinating widely and others lagging. Perkins blames a perception problem: “The biggest misconception from families is that the HPV vaccine is not needed or that it can wait,” she said. “The reality is that you can’t vaccinate too early, only too late.” And on hepatitis B, the U.S. is arguably walking backwards — the Centers for Disease Control and Prevention recently decided to stop recommending universal vaccination at birth, a move experts say could raise hepatitis B infections and, eventually, the cancers that follow them.
The hard cases
Epstein-Barr is the opposite problem: there is no approved vaccine at all, and making one is genuinely hard. “The biggest hurdle has been the complexity of the virus,” Claire Shannon-Lowe, a tumor virologist at the University of Birmingham who was not involved in the study, told Live Science. “Unlike many other viruses that use just one or two virus proteins to enter cells, EBV uses multiple proteins ... and it hides inside cells for our entire lifetime.” It also infects up to 95% of people by adulthood, the vast majority of whom never develop a related cancer — which makes “cancer prevention,” on its own, a tricky pitch for a mass EBV vaccination campaign.
What might get the vaccine built is that EBV has been racking up other charges, including associations with autoimmune diseases like multiple sclerosis and lupus. A shot that prevents some lymphomas is a niche product; a shot that might also fend off MS is a business. “With the increased impetus following EBV’s association with multiple sclerosis and lupus, we may finally have a potential vaccine in sight that could not only prevent virus infection but could help treat EBV-associated cancers,” Shannon-Lowe said.
Cancer is famously the disease with no simple answer. Except that for about one case in eight, the answer exists and is a shot, a distribution network and, apparently, a follow-up appointment nobody schedules. The science turned out to be the easy part.