Study details and key findings

For the study, researchers from the World Health Organization's International Agency for Research on Cancer (IARC) analyzed national estimates of new cancer cases in 2024 among people of all ages from the Global Cancer Observatory's Cancer Today database and other registries.

For all cancers in 2024, the age-standardized incidence rate of cases caused by infectious agents was 22.7 per 100,000 person-years. The researchers estimated that 12 infectious agents, which are classified as Group 1 carcinogens by IARC's Cancer Monographs Program, contributed to a significant portion of new cancer cases.

Of these infectious agents, those associated with the most cancer cases were:

• Helicobacter pylori: 760,000 cases, mostly non-cardia gastric cancers (4%)
• Human papillomavirus: 750,000 cases, mostly cervical cancer (4%)
• Hepatitis B virus: 360,000 cases, mostly hepatocellular carcinoma (2%)
• Epstein-Barr virus: 260,000 cases, mostly nasopharyngeal cancers (1%)
• Hepatitis C virus: 160,000 cases, mostly hepatocellular carcinoma (<1%)
• Kaposi's sarcoma-associated herpesvirus (KSHV): 35,000 cases (<1%)

Overall, infections were responsible for around 12% of new cancer cases worldwide, or roughly 2.3 million cases, in 2024.

According to the Washington Post, this proportion is similar to what IARC found in a similar study in 2018. At the time, researchers estimated that around 13% of new cancer cases were due to infections.

Lorelei Mucci, a professor of epidemiology at Harvard University who was not involved in the study, said it was "alarming" that the proportion of new cancer cases caused by infections had not changed since the 2018 study.

"That's really a failure of public health," Mucci said. "We really know how to prevent a lot of these cancers from happening by preventing the infection."

Harriet Rumgay, an epidemiologist at IARC and one of the study's authors, cautioned against directly comparing the two studies since the most recent one included a broader range of cancers associated with infectious diseases. However, she agreed that the trends have largely remained the same over time.  

How to prevent infections and lower your risk of cancer

However, growing vaccine hesitancy and changes to vaccination schedules in the United States could impact the risk of cancer from infections. Both the HPV and hepatitis B vaccines have been part of the Trump administration's overhaul of childhood vaccine recommendations.

Some infections, such as Epstein-Barr virus, currently have no effective prevention tools.

"A major priority is the development of vaccines against [Epstein-Barr virus], which causes several cancers and has also been linked to multiple sclerosis," Rumgay said. New prevention tools are also needed for KSHV, especially because resource-limited countries in sub-Saharan Africa face the greatest cancer burden related to the virus.

Globally, differences in infection prevalence, healthcare infrastructure, vaccination coverage, and more could also impact efforts to reduce infections and the risk of cancer. "[T]here is no single prevention strategy that will work equally well everywhere," Rumgay said. "As a result, prevention strategies need to be tailored to local infection and disease patterns and healthcare needs, while ensuring equitable access to effective interventions."

Overall, the study's findings "underscore the importance of accelerating control of infectious agents to achieve cancer prevention goals," the researchers wrote.