Roughly 1 in 8 cancer cases worldwide may be linked to infections, according to research published in The Lancet Oncology. The findings indicate that millions of cases could potentially be avoided through vaccination, screening, testing or treatment.

Researchers estimated that infections accounted for about 2.3 million new cancer cases globally in 2024, equal to 12% of all diagnoses. The study examined cancer incidence data from the Global Cancer Observatory’s Cancer Today database.

The team assessed how many cases could be attributed to infections and analyzed each pairing between an infection and a type of cancer. Two infections, Helicobacter pylori and human papillomavirus, accounted for more than 1.5 million cases together.

H. pylori was associated primarily with gastric cancers, while HPV was linked predominantly to cervical cancer. Both infections can be addressed through established prevention or treatment strategies.

“We can intervene before it gets anywhere near cancer,” said Gary Clifford, the study’s senior author and an epidemiologist at the International Agency for Research on Cancer.

“We just need the politics and the finances and the buy-in from the public and the communication to get the programs implemented. Prevention works,” Clifford said. “It’s an awareness-raising issue.”

Hepatitis B was linked to an estimated 360,000 cancer cases, mostly liver cancers. The Epstein-Barr virus was associated with about 260,000 cases, with a head and neck cancer beginning in the nasopharynx as the main contributor.

Hepatitis C was tied to 160,000 cases, again mostly involving liver cancer. The analysis included 16 additional pairings between infections and cancers compared with an earlier global analysis published in 2018.

The researchers said scientific understanding of the connections between certain infections and cancer has improved. Clifford noted that EBV was the first infectious agent discovered to cause cancer, initially through its connection to Burkitt lymphoma.

“Some infection-related cancers, such as liver and gastric cancer, generally have poor prognosis, meaning that a similar proportion of deaths from these cancers are likely attributable to infection. For other cancers, including cervical cancer and Kaposi sarcoma, infection is necessary for cancer development,” study author Harriet Rumgay said in an email.

Rumgay, an epidemiologist at the International Agency for Research on Cancer, said highly effective prevention measures exist for four of the five leading infectious causes of cancer, as well as HIV. Vaccines are available for HPV and hepatitis B, while testing and treatments are available for H. pylori and hepatitis C.

The worldwide burden was distributed unevenly. Low income and middle income countries accounted for 77% of all cancer cases attributed to infections, reflecting differences in infection prevalence and access to vaccination, screening, testing and treatment.

Disparities also exist within the United States, according to Veronika Fedirko, a professor of epidemiology at The University of Texas MD Anderson Cancer Center who was not involved in the study. She said some populations have higher rates of hepatitis B, hepatitis C, HPV or H. pylori, while others have less access to preventive services and treatment.

A separate American Cancer Society analysis found that 3.4% of cancers among adults 30 and older in 2019 were attributable to seven infections evaluated. That represented about 60,310 cases, with HPV identified as the largest contributor.

“Having a cancer-causing infection does not mean that a person will develop cancer. These infections increase the risk of certain cancers, but most people who are infected will never develop cancer,” Fedirko said.

She explained that cancer generally develops in a small proportion of infected people, often after an infection persists for years and alongside factors such as age, immune function, smoking, genetics or other exposures. Cancer also has numerous other causes and risk factors, including aging, lifestyle and environmental exposures.

Testing and treatment can interrupt that progression. People with hepatitis C can receive treatment, while antibiotics can treat H. pylori, a relatively common bacterium that can cause chronic stomach inflammation and increase stomach cancer risk.

Vaccination offers another major opportunity. The hepatitis B vaccine can prevent an infection that may damage the liver over time, while HPV vaccination can help prevent cervical, anal, penile, vaginal, vulvar and oropharyngeal cancers by preventing HPV infection.

“This is no different than getting your flu shot to prevent the flu. The public needs to be made aware and vaccination should be reinforced,” said Dr. Nancy Lee, a radiation oncologist at Memorial Sloan Kettering Cancer Center who was not involved in the research.

Other measures include “safe injection practices, condom use, and HIV pre-exposure prophylaxis,” Rumgay said. She added that widespread and equitable implementation could prevent hundreds of thousands, or potentially millions, of future cancer cases worldwide.