Can You Prevent the Infections Behind 1 in 8 Cancers?
Most of the infections behind the "1 in 8 cancers" headline are preventable or treatable. Four pathogens do almost all the damage: Helicobacter pylori, HPV, hepatitis B, and hepatitis C. For each, there's a specific move with real human evidence: a vaccine, a stool or blood test, a short course of pills. The size of the effects is unusual. Vaccinating against HPV before age 17 cuts invasive cervical cancer by around 80 to 88 percent. The useful question isn't the global percentage. It's which of the four applies to you, and whether you've acted on it.
The new IARC analysis in The Lancet Oncology attributes about 2.3 million of the roughly 20.6 million cancers diagnosed worldwide in 2024 to infections. The breakdown is lopsided. H. pylori accounts for around 760,000 cases, HPV for 750,000, hepatitis B for 360,000, and hepatitis C for 160,000. Everything else combined is a small minority. That concentration is what makes the headline personal. If the burden spanned dozens of microbes, this would be a policy problem. Four names turn it into a checklist.
The effect sizes aren't modest
HPV vaccination and H. pylori eradication are two of the biggest single-intervention wins in cancer prevention. Nationwide registry studies from Sweden, Denmark, England, and Scotland show that vaccinating girls before age 17 cuts invasive cervical cancer by about 80 to 88 percent, and the 9-valent formulation covers the strains behind roughly 90 percent of cervical cancers worldwide. H. pylori eradication is in the same league. Pooled randomized trials show about a 36 to 46 percent drop in gastric cancer in people who are treated, and about half as many second cancers in people who've already had one removed. These are closer to polio-era numbers than to the small effects of most lifestyle advice.
The benefit is front-loaded
When you act matters more than most people assume. The 88 percent figure applies to HPV vaccination before sexual debut. Vaccinate after 17 or 20 and the effect drops to around 37 to 53 percent, because many people have already met the common strains. H. pylori works the same way. Treatment is strongest before the stomach lining has started its slow slide toward cancer. Once pre-cancerous changes like intestinal metaplasia are in place, eradication still helps, but it doesn't reverse them.
More testing doesn't always pay off. Mass eradication of H. pylori in unselected adults from low-prevalence settings hasn't been shown to lower all-cause mortality in pooled randomized trials, and the costs are real: about a 6 percent rise in reflux esophagitis after therapy, gastrointestinal side effects, and more antibiotic resistance in the population. The usable rule is to match the right person to the right intervention early enough that it works.
The four pathogens, and what to do about each
| Pathogen | Main cancer(s) | What to do | What the evidence shows |
|---|---|---|---|
| HPV | Cervical, anogenital, oropharyngeal | 9-valent vaccination, ideally before age 17 (routine at 11-12, can start at 9; catch-up through 26; shared decision 27-45) | About an 80 to 88 percent drop in invasive cervical cancer when given before 17; roughly 37 to 53 percent after 17 to 20 |
| H. pylori | Non-cardia gastric cancer, gastric MALT lymphoma | Stool or breath test if you have indigestion or stomach pain, a family history of gastric cancer, or grew up in East Asia, Latin America, or sub-Saharan Africa; then a 14-day bismuth quadruple therapy course with a test of cure 4 or more weeks later | About a 36 to 46 percent cut in gastric cancer; roughly half the recurrence after a prior tumor is removed |
| Hepatitis B | Liver cancer | Vaccination for all adults 19-59; one-time hepatitis B blood test if you were born in a region where chronic hepatitis B runs 2 percent or higher, or have other USPSTF risk factors | Vaccination prevents chronic infection; finding chronic infection enables antiviral treatment and liver cancer surveillance |
| Hepatitis C | Liver cancer | One-time antibody blood test for every US adult 18 to 79 | Direct-acting antivirals cure the infection; residual liver cancer risk remains if cirrhosis has already developed |
Who's missing the benefit
HPV vaccination still skips many of the adolescents it would help most, and catch-up through age 26 is uneven. H. pylori testing is usually offered only after indigestion or an ulcer brings someone in. If you grew up in East Asia, Latin America, or sub-Saharan Africa, or have a family history of gastric cancer, you typically won't be tested unless you ask. One-time hepatitis C screening for every US adult has been standard since 2020, and many people still haven't been offered it. Hepatitis B screening is risk-based rather than universal, so people born where chronic hepatitis B runs 2 percent or higher often slip through.
The gap isn't the science. The timing is: vaccinate early, treat early, act before the damage is there. Most of the people who could benefit don't know they're on the list.