A new report from the World Health Organization's International Agency for Research on Cancer, published in The Lancet Oncology, found that 12% of new cancer cases in 2024 — the most recent year with available data — were caused by 12 infections classified as Group 1 human carcinogens.

Time reports that HPV and Helicobacter pylori each accounted for about 4% of new diagnoses, hepatitis B for 2%, EBV around 1%, and hepatitis C for less than 1%, with seven other infections including HIV also flagged as carcinogens.

clarin.com reports the total as an estimated 2.3 million cases worldwide, meaning roughly 1 in 8 cancers globally is linked to an underlying infection.

The surprise is scale and persistence: clarin.com notes the global proportion of infection-attributable cancers has remained essentially unchanged since IARC's previous 2018 assessment, which estimated 13%.

Cancer often seems random — the product of accumulated DNA damage and genetic predisposition — but these findings show a large, largely preventable share of malignancies traces back to common viruses and bacteria.

clarin.com also reports stark inequities: low- and middle-income nations bear 77% of all infection-attributable cancer diagnoses, with Eastern Asia accounting for 990,000 cases, or 42% of the global total.

According to clarin.com, the vast majority of infection-driven cancers in 2024 were concentrated among five pathogens.

H. pylori was linked to 760,000 cases, including 700,000 of non-cardia gastric cancer; HPV to 750,000 cases, including all 600,000 cervical cancers; hepatitis B to 360,000 liver cancers; EBV to 260,000 cases including nasopharyngeal carcinoma and Hodgkin lymphoma; and hepatitis C to 160,000 cases.

Time explains the mechanisms differ: H. pylori causes chronic tissue damage and toxins that destabilize cell-growth control, while virologist Claire Shannon-Lowe tells Time that EBV hides inside B cells and manipulates them into continually growing.

Many of these cancers are preventable with tools that already exist, according to clarin.com: the hepatitis B vaccine — which Time reports was the first vaccine developed against cancer — is given to infants within 24 hours of birth; the HPV vaccine, approved 20 years ago, offers near-complete protection against high-risk strains; H. pylori can be cleared with antibiotics and breath or stool tests; and direct-acting antivirals cure hepatitis C in over 95% of patients within 8 to 12 weeks.

But clarin.com reports hepatitis B vaccination rates in U.S. newborns have declined steeply over the last two years, and Time notes these vaccines are not reaching everyone who might benefit.

Epidemiologists expect vaccination's effects to show up soon in the data: IARC's Harriet Rumgay tells Time that more and more people vaccinated against HPV are reaching the ages where impacts on cervical and other cancer rates could become visible in future analyses.

For EBV — a virus carried by more than 90% of the world's population — no approved vaccine exists, but Time reports that interest has grown partly because of research linking EBV to multiple sclerosis, and several candidate vaccines are now in clinical trials.

Rumgay also tells Time that Kaposi's sarcoma-associated herpesvirus, in particular, needs much more prevention research, and she hopes the new findings will stimulate development in that area.