Millions of cancer cases worldwide, about 1 in 8, have an underlying cause that is not only treatable but preventable altogether, according to a new study.
The answer lies in infections, according to research published this month in The Lancet Oncology, including two of the most common infections in the United States. Roughly 12% of new cancer cases reported globally in 2024 could be traced back to just 12 infections, the authors found, meaning roughly 2.3 million cancer illnesses worldwide could potentially have been prevented.
Five of those infections accounted for more than 2.2 million of the estimated 2.3 million infection-attributable cancer cases recorded in the study, and two — the common stomach infection H. pylori and the sexually transmitted HPV — were behind about 1.5 million.
The good news? According to the researchers, we already know how to stop and treat these infections. The bad news? In some countries, that’s not happening.
Five Infections Account for Most Cases
The study identified these five infections as responsible for most infection-related cancer cases:
- Helicobacter pylori (H. pylori): A common stomach infection that can cause stomach pain, bloating, gas and similar symptoms. More than half of the world’s population may have an H. pylori infection at some point in their lives, according to Mayo Clinic. It was most associated with gastric cancers in the study (approximately 760,000 cases, or 4% of new cancer diagnoses worldwide).
- HPV (human papillomavirus): A common infection with more than 100 types, HPV is the most common viral sexually transmitted infection in the United States, infecting roughly 14 million people a year, according to Cleveland Clinic. Some strains are high-risk factors for certain cancers, including cervical, vaginal and vulvar. It was most associated with cervical cancer in the study (approximately 750,000, or 4%, of new cases). There is a vaccine that is ideally given before a person becomes sexually active.
- Hepatitis B (HBV): A vaccine-preventable, often asymptomatic liver infection that can range from a short, acute illness to a serious, chronic infection, according to the CDC. Acute infections are more common in people between the age of 40 and 59. It was most associated with liver cancers (approximately 360,000, or 2%, of new cases).
- Epstein-Barr virus (EBV): A very common viral infection and type of herpesvirus that often does not cause symptoms and most affects children, teens and young adults. Up to 95% of adults experience an EBV infection in their lifetime, according to Cleveland Clinic. It was most associated with cancers of the head and neck (approximately 260,000, or 1%, of new cases).
- Hepatitis C (HCV): A viral infection that causes liver inflammation and can lead to serious damage. Like hepatitis B, it can cause a short, acute illness or a chronic, long-term one. It is often asymptomatic; experts estimate that more than 2 million people have chronic hepatitis C in the U.S., according to Cleveland Clinic. It was most associated with liver cancers (approximately 160,000, or just under 1%, of new cases).
Other infections identified as linked to cancer included HIV, Kaposi’s sarcoma-associated herpesvirus, Schistosoma haematobium (a blood parasite common in Africa and the Middle East), human T-cell lymphotropic virus type 1, Opisthorchis viverrini (a liver parasite found in Southeast Asia), Clonorchis sinensis (another liver parasite from Southeast Asia) and Merkel cell polyomavirus, a virus known primarily for causing cancer.
How to Read the Study’s Estimates
The study doesn’t track every individual cancer case. Instead, it uses global cancer data and previous research to estimate how many cancers are linked to infections. The authors say the figures are the best available estimates, but gaps in cancer reporting in some parts of the world mean the totals aren’t exact. The study counts only infections already known to have some association with cancer; others may not yet have enough evidence to establish a link.
Cancer registries are less complete in some regions, particularly in lower-income countries, making it difficult to measure the true global burden of infection-related cancers. The study found that 77% of infection-related cancer cases occurred in low- and middle-income countries. Eastern Asia, sub-Saharan Africa and Southeast Asia were among the regions with the largest cancer burden.
While 12% of global cancer cases is a significant share, most cancers are not caused by infection, at least according to what scientists know now.
Prevention Can Reduce Some Cancer Risks
Infection may not be the primary driver behind most cancers, but it accounts for a disproportionate number of cases of certain types, such as cervical cancer. The study found that the vast majority of cervical cancer cases can be attributed to HPV.
Researchers noted that several cancers could be prevented with tools already available. In these cases, infection control, which is a well-established science, could lead to cancer control.
The authors said more research is needed, especially for some infection-cancer relationships still being explored, such as Epstein-Barr. But proven methods can address certain risks. The researchers found that areas with the highest cancer burden do not have as ready access to the resources used to track, prevent and control infection.
- HPV vaccination is a major prevention tool, the study authors said. CDC data show it can be highly effective in preventing both infections and associated cancers.
- Within 12 years of the vaccine Gardasil being introduced in the United States, infections of the four HPV types it targets decreased 88% among 14- to 19-year-old females and 81% among 20- to 24-year-old females.
- Cervical precancer rates among screened females dropped 50% in 18- to 20-year-olds and 36% in 21- to 24-year-olds in the six years after Gardasil hit the market. Cervical lesions due to HPV types prevented by vaccination dropped by 40% in vaccinated women after vaccines were introduced.
- Vaccination against hepatitis B is also available and is recommended by the CDC for all infants, children and adults ages 19 to 59, as well as adults ages 60 and older at high risk for infection. Vaccination reduces the risk of liver cancer linked to HBV infection. The CDC says each adult should be tested at least once in their lives for hepatitis B; those at higher risk should be tested regularly.
- More frequent testing and treatment for H. pylori, which can include stool, breath or scope screenings and antibiotics, can reduce its spread and prevalence and therefore its likelihood of contributing to cancer.
- Testing and treatment for hepatitis B, hepatitis C and HIV can help reduce transmission and prevent infections from becoming chronic, which can increase cancer risk.
- Safer injection practices, condom use, PrEP use and making the tools for these practices more available can help stop the transmission of HIV, hepatitis B and hepatitis C.
- Screening and treatment of precancerous lesions, especially in cases of HPV-related cervical and anal cancer, can help with early diagnosis and better cancer-related outcomes.
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