About 2.3 million of the cancers diagnosed worldwide in 2024 were attributable to infection with a virus, a bacterium or a parasite. That is roughly one in eight, or 12 percent, of all new cases, by the estimate of the International Agency for Research on Cancer (IARC), the World Health Organization’s cancer research arm.
The IARC attribution: 2.3 million cases in 2024
The figure is an attribution estimate, not a tally of patients who tested positive for a pathogen: it assigns a share of each cancer type in each region to the infections known to cause it. The analysis was published in The Lancet Oncology on September 28, 2026, and Harriet Rumgay of IARC is among its authors and the agency’s voice on the findings. Because the underlying year is 2024, the estimate describes the burden of that year, and later years will differ.
IARC’s published question-and-answer document carries the central numbers: one in eight, about 2.3 million cases, in 2024. The percentage is a global average that conceals large differences, and the same analysis reports that low- and middle-income countries carry roughly three-quarters of the infection-linked burden.
The five pathogens, and the four that dominate
Five infectious agents account for nearly all of it, according to the IARC figures. Helicobacter pylori, a stomach bacterium, is linked to about 760,000 cases, mainly gastric cancer. Human papillomavirus (HPV) accounts for about 750,000, covering cervical, anal, vulvar, vaginal and penile cancers and some cancers of the head and neck. Hepatitis B virus accounts for about 360,000, mostly liver cancer. Epstein-Barr virus is tied to about 260,000, among them nasopharyngeal cancer, some stomach cancers and Hodgkin lymphoma. Hepatitis C virus, mainly through liver cancer, adds about 160,000.
The first four of those make up roughly 92 percent of infection-related cancers worldwide, as Live Science reported from the paper, which means the problem is concentrated in a short list of pathogens rather than spread across dozens.
The geography is lopsided as well. East Asia recorded about 990,000 of the cases, around 42 percent of the global total, driven largely by H. pylori and hepatitis B, according to Euronews. In Sub-Saharan Africa, about a quarter of all cancers are linked to infection, the highest share of any region, with HPV and the HIV and KSHV viruses prominent. Rumgay said that despite progress in vaccination and screening, infection-related cancers remain a major global challenge, with the burden falling disproportionately on low- and middle-income populations.
Vaccines, screening and treatment against the burden
An infection-driven cancer differs from most others in one practical respect: the cause can be intercepted before the tumour ever forms, by vaccine, by treatment of the infection or by finding precancerous change early. IARC lists vaccination against HPV and hepatitis B, testing and treatment for bacterial and viral infections, screening and measures to prevent transmission as the routes by which a significant proportion of the global cancer burden is preventable.
Cervical cancer shows how the chain works. The WHO fact sheet states that almost all cervical cancer is caused by infection with cancer-causing HPV types, a process that typically takes 15 to 20 years from persistent infection, or 5 to 10 years in people with weakened immunity. WHO’s elimination targets, set for 2030 and framed around three numbers, are 90 percent of girls vaccinated by age 15, 70 percent of women screened by ages 35 and 45, and 90 percent of women with precancer or cancer treated. The fact sheet also reports that women living with HIV are six times more likely to develop cervical cancer than women without it.
The United States Centers for Disease Control and Prevention reports that HPV causes about 39,300 cancers there each year and that vaccination and cervical screening can help prevent them, on its HPV and cancer page. Dr. Rebecca Perkins, quoted by Live Science, pointed to the payoff where vaccination has been fast: cervical cancer is starting to disappear in countries that reached vaccination rates above 80 percent.
Outside researchers read the estimate as a confirmation more than a surprise. Ramón Salazar of the Catalan Institute of Oncology said it is in line with previous trends and should serve as a guide for global planning on primary prevention, and Silvia de Sanjosé of ISGlobal said it significantly increases the contribution of infections as a cause of cancer, as the Science Media Centre in Spain compiled them.
One caution applies to any single global ratio. IARC’s 2024 attribution is an average across regions where the main causes differ sharply, from stomach bacteria and hepatitis B in East Asia to HPV and HIV-related viruses in Sub-Saharan Africa, so the one-in-eight share says little about the risk in any single country.
This article was produced with the assistance of AI and reviewed by Morning Overview editors prior to publication.
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