By Diane Wheaton
Most people associate cancer with genetics, smoking, environmental exposures or simply bad luck. An infection probably isn’t the first thing that comes to mind. After all, infections are something we generally expect to recover from, whether it’s a virus that makes us feel miserable for a week or a bacterial infection that requires treatment. But a newly published study is drawing attention to a connection that many people may not realize exists: certain infections can contribute to the development of cancer, sometimes many years after the original infection.
In September 2026, the World Health Organization’s International Agency for Research on Cancer released findings from a major study published in The Lancet Oncology. Researchers estimated that approximately one in eight new cancer cases worldwide in 2024, representing 2.3 million diagnoses, could be attributed to infections. The findings don’t suggest that everyday illnesses routinely lead to cancer. Instead, they highlight the role of specific viruses, bacteria and parasites that scientists have identified as cancer-causing agents.
The research is especially interesting because it changes how we might think about cancer prevention. While many cancers develop through a complicated combination of inherited characteristics, environmental exposures and other influences, some have a connection to infections that can potentially be prevented, identified or treated.
How Can an Infection Lead to Cancer?
To understand the connection, it helps to know a little about how cancer develops. Our bodies are constantly producing new cells to replace old or damaged ones. Normally, this process is carefully regulated. Cells grow, divide and eventually die according to instructions built into their DNA. Cancer can develop when changes interfere with those instructions, allowing abnormal cells to multiply without the usual controls.
Certain infectious organisms can interfere with this process. Some viruses affect the machinery that controls cell growth, while other infections produce long-lasting inflammation that damages surrounding tissue. Over time, these changes may contribute to the conditions in which cancer develops.
The important words here are “may contribute.” Most people who encounter an infection associated with cancer will never develop the disease. The presence of an infection is not the same as a cancer diagnosis, and even persistent infections do not automatically lead to cancer.
The Common Infections Behind the Research
One of the most significant findings involves a bacterium called Helicobacter pylori, commonly known as H. pylori. This organism can live in the stomach lining and is best known for its association with certain stomach ulcers. Many people carrying it have no noticeable symptoms, which means they may not realize an infection is present.
In some individuals, however, H. pylori produces persistent inflammation in the stomach lining. Over many years, that inflammation can contribute to cellular changes associated with stomach cancer. The infection is also linked to a less common cancer involving immune cells in the stomach, known as gastric MALT lymphoma.
Another major contributor is human papillomavirus, or HPV. Although HPV is often discussed in connection with cervical cancer, its role extends further. Certain high-risk types are associated with cancers of the throat, anus, penis, vulva and vagina. HPV is extremely common, and the immune system clears or controls most infections without lasting consequences. The concern arises when particular high-risk types persist and interfere with normal cellular processes. Even then, cancer is not inevitable. The progression from persistent infection to cancer generally takes years, and additional biological factors influence whether it occurs.
Hepatitis B and hepatitis C are also important because of their relationship to liver cancer. Both viruses can cause long-term liver infections, sometimes without obvious symptoms. Persistent infection may gradually damage the liver, producing inflammation and scarring that increase cancer risk. Hepatitis B can also contribute to cancer through effects on infected cells.
These examples demonstrate why infection-related cancers aren’t confined to one organ or one part of the body. Different infectious agents affect different tissues, and their biological effects vary considerably.
What About the Epstein-Barr Virus?
One particularly interesting name in the research is Epstein-Barr virus, often abbreviated EBV. Many people have encountered this virus without knowing it. It’s best known for causing infectious mononucleosis, sometimes called mono, although infection frequently produces few or no noticeable symptoms.
EBV remains in the body after the initial infection, usually under the control of the immune system. In certain circumstances, it can contribute to the development of particular cancers, including some lymphomas and cancers involving the upper throat and stomach. The connection may sound unsettling given how widespread EBV infection is. But context matters. Most people infected with EBV never develop an EBV-related cancer. Scientists are still investigating why a virus that is so common contributes to malignancy in only a relatively small proportion of infected individuals.
Why the Findings Matter
Although the research describes a worldwide problem, the burden of infection-related cancers is not evenly distributed. Rates differ considerably among countries because of variations in infection prevalence, vaccination programs, sanitation, access to healthcare and the availability of screening and treatment. Some regions experience much higher rates of certain infection-related cancers than others. For example, stomach cancer associated with H. pylori and liver cancer associated with hepatitis viruses create substantial health burdens in parts of Asia.
This is why the worldwide estimates shouldn’t be interpreted as an individual’s personal cancer risk or assumed to represent the exact proportion of cancers occurring in the United States. The findings also illustrate something encouraging about cancer research. Scientists aren’t simply learning more about how cancers develop. They’re identifying opportunities to interrupt some of the processes that contribute to them.
Where Prevention Enters the Picture
Perhaps the most promising aspect of infection-related cancer research is that some of the contributing infections can be addressed before cancer develops.
Vaccination has already changed the outlook for diseases associated with certain viruses. HPV vaccination protects against important cancer-causing types of HPV, while hepatitis B vaccination helps prevent infection with a virus associated with liver cancer.
Screening also has a role. Cervical cancer screening can identify abnormal cellular changes associated with persistent high-risk HPV infection, often before cancer develops. Testing and treatment for certain infections, including H. pylori and hepatitis C, may also help reduce future complications in appropriate circumstances.
The American Cancer Society explains that infections can contribute to cancer through several mechanisms and identifies vaccination, infection treatment and recommended screening as important parts of reducing certain infection-associated cancer risks.
These measures aren’t interchangeable, and they don’t apply to everyone in the same way. Eligibility for vaccination, screening and testing depends on factors such as medical history, previous immunizations and individual circumstances. A healthcare professional can help determine which preventive services are appropriate.
It’s also worth remembering that preventing an infection-associated cancer doesn’t mean every cancer can be prevented. Cancer remains a complex group of diseases, and many cases arise through mechanisms unrelated to infectious organisms.
A Different Perspective on Cancer
The discovery that certain infections can contribute to cancer has already influenced medicine in meaningful ways. It has helped scientists better understand how cells become cancerous and has contributed to preventive strategies that would have seemed remarkable in earlier generations.
The latest findings build on decades of research rather than overturning everything previously understood about cancer. Their value lies in providing a more complete picture of the global burden and identifying where prevention efforts may have the greatest impact.
For individuals, the message is considerably less complicated than the science behind it. Not every infection is dangerous in the long term, and most infections linked to cancer never result in a malignancy. There is no reason to interpret an ordinary cold, stomach bug or past illness as evidence of an impending cancer diagnosis.
What the research does offer is another reason to appreciate the importance of preventive healthcare and informed conversations with medical professionals. Knowing which infections are associated with cancer, understanding the purpose of recommended screenings and staying informed about established prevention measures can help people approach their health with greater confidence.
