12% of Cancer Cases Are Linked to Infections. These 5 Are Behind Nearly All of Them

Cancer is usually discussed in terms of genetics, smoking, alcohol, obesity, environmental exposures, or simply bad luck. But one major cause receives far less attention: infection.

A new global analysis estimates that viruses, bacteria, and other infectious agents were responsible for approximately 2.3 million new cancer cases in 2024, about 12% of all cancers diagnosed worldwide.

Even more striking, nearly all of that enormous burden could be traced back to just a handful of pathogens.

The study, published in The Lancet Oncology by researchers at the International Agency for Research on Cancer (IARC), identified five infections as the dominant contributors: Helicobacter pylori, human papillomavirus (HPV), hepatitis B virus (HBV), Epstein-Barr virus (EBV), and hepatitis C virus (HCV).

Some are extraordinarily common. Roughly half the world’s population carries H. pylori, often without knowing it. HPV infections are so widespread that most sexually active people will encounter the virus at some point. EBV eventually infects the vast majority of adults.

For most people, these infections will never lead to cancer. But in a smaller proportion, persistent infection can alter cells, promote chronic inflammation, or interfere with the body’s normal defenses against abnormal cell growth.

That also makes infection-related cancers unusual in another important way: some can potentially be prevented before cancer ever develops, through vaccination, screening, testing, or treatment of the underlying infection.

Here are the five infections responsible for the overwhelming majority of that global burden, and what scientists know about reducing the risk.

The five infections causing cancer globally

1. Helicobacter pylori: The bacterium in half the world

The leading infectious cause of cancer in 2024 was Helicobacter pylori, linked to around 760,000 cancer cases globally that year. That figure represents 4% of all cancer diagnoses worldwide.

The sheer prevalence of this infection is what makes it so consequential. Approximately half the world’s population carries H. pylori, and for the vast majority the infection remains completely silent. Certain strains, however, can cause gastric ulcers and ultimately stomach cancer – and chronic infection with H. pylori is the dominant driver of gastric cancer globally.

Gary Clifford explained that many of these infections “hijack the cellular machinery that controls the normal cell cycle in order to help their own replication – however, this includes hijacking the machinery that would normally repair mutated genes or instruct mutated cells to die, thus increasing the risk for mutated cells to become immortal,” which is the defining characteristic of cancer.

According to the National Cancer Institute, H. pylori is the only confirmed bacterial carcinogen, making it unique among the five pathogens on this list. Treatment exists – antibiotics can eradicate the infection – but the challenge isn’t a lack of treatment options. Reaching the populations most affected, particularly in Asia and sub-Saharan Africa where infection rates and gastric cancer mortality remain highest, is the central implementation problem.

2. Human papillomavirus (HPV): Far more than cervical cancer

Human papillomavirus (HPV) was linked to 750,000 cancer cases in 2024. Like H. pylori, it accounted for roughly 4% of all cancers diagnosed that year, placing the two pathogens in a near-statistical tie as the dominant infection-related cancer causes.

HPV causes virtually all cervical cancer, and routine screening with an HPV test or Pap smear can prevent most cervical cancer by allowing providers to find and remove precancerous cells before they develop into malignancy. Beyond the cervix, the National Cancer Institute documents HPV as responsible for 70% of oropharyngeal (throat) cancers, 91% of anal cancers, and the majority of vaginal, vulvar, and penile cancers.

Cervical cancer is the fifth most common cancer in women worldwide, with rates concentrated in countries with limited screening access, according to the WHO’s cervical cancer fact sheet.

Men remain significantly under-vaccinated against HPV globally. The IARC study authors specifically flagged the need to expand vaccination coverage in men, who are disproportionately affected by HPV-related oropharyngeal cancers and who can transmit the virus to partners without knowing they carry it.

3. Hepatitis B virus (HBV): A preventable liver cancer driver

Hepatitis B virus (HBV) was linked to 360,000 cancer cases in 2024 – roughly 2% of the global total. The overwhelming majority of those cases are hepatocellular carcinoma, commonly known as liver cancer.

Chronic HBV infection is a leading cause of cirrhosis and liver cancer globally. Cirrhosis is the gradual scarring of the liver; when driven by HBV, it creates a tissue environment where cancer is far more likely to develop. Eastern Asia bears a disproportionate share of this burden, with H. pylori and HBV together driving the regional concentration of infection-linked cancers.

A safe and effective HBV vaccine has been available since the 1980s and is now part of childhood immunization schedules in most countries. The IARC scientists stated that policy-makers and health systems should prioritize scaling up proven interventions, including vaccination against HBV, testing and treatment for HBV and HCV, and measures to prevent transmission such as safe injection practices and access to condoms.

4. Epstein-Barr virus (EBV): The most common virus you’ve never heard of

Epstein-Barr virus (EBV) was linked to 260,000 cancer cases in 2024 – roughly 1% of all global cancer diagnoses. EBV is new to the IARC’s formal accounting of infection-attributable cancers; the evidence linking it directly to malignancy has grown substantially since the previous global estimates were published.

Approximately 95% of adults worldwide are latently infected with EBV. The virus is associated with nasopharyngeal carcinoma, Hodgkin’s lymphoma, Burkitt’s lymphoma, certain gastric cancers, infectious mononucleosis, and post-transplant lymphoproliferative disorders. Nasopharyngeal carcinoma is a cancer of the upper throat, behind the nose, and is particularly prevalent in East and Southeast Asia.

No effective EBV vaccine has been approved for clinical use, though multiple platforms – including subunit vaccines, viral vector-based formulations, nanoparticle-based approaches, and mRNA vaccines – are under active investigation. The National Institute of Allergy and Infectious Diseases (NIAID) has launched an early-stage clinical trial to evaluate an investigational preventive EBV vaccine. Until an approved vaccine exists, there are no population-level tools to prevent EBV infection or halt its spread.

5. Hepatitis C virus (HCV): A smaller but significant footprint

Hepatitis C virus (HCV) was linked to less than 1% of global cancer cases in 2024, with cases concentrated almost entirely in liver cancer, where HCV operates through the same chronic inflammation and cirrhosis pathway as HBV.

Unlike HBV, there is no vaccine for HCV. Direct-acting antiviral medications introduced in the 2010s can now cure the large majority of HCV infections. The challenge, as with the other pathogens, is access: these antivirals and screening programs remain least available in the settings where infection rates are highest.

The geographic inequity behind the numbers

Three-quarters of infection-related cancers came from low-income and middle-income countries, predominantly in eastern Asia, African nations south of the Sahara, and southeastern Asia. Eastern Asia alone accounted for 42% of infection-linked cancer diagnoses in 2024, driven mainly by H. pylori and HBV.

That concentration reflects the intersection of high pathogen prevalence, limited vaccination coverage, constrained screening infrastructure, and restricted access to curative treatments. Harriet Rumgay noted that “despite progress in vaccination and screening, infection-related cancers remain a major global challenge, with the burden falling disproportionately on populations in low- and middle-income countries.”

The science of prevention is largely established – vaccines for HPV and HBV exist and work, H. pylori can be tested and treated, HCV can be cured. Sub-Saharan Africa and East Asia are not experiencing more infection-linked cancers because their populations are more susceptible; they are experiencing more because the interventions that can prevent those cancers are not reaching them at adequate scale.

How infections drive cancer at the cellular level

Chronic infection from each of these pathogens produces chronic inflammation, which damages the genetic machinery that keeps cells replicating normally.

H. pylori physically damages gastric mucosa – the lining of the stomach – and triggers an inflammatory response that, over years or decades, can progress from gastritis to precancerous lesions. HPV uses a different mechanism: high-risk strains produce proteins (designated E6 and E7) that disable two of the body’s core tumor-suppressor systems, effectively removing the cellular brakes that prevent abnormal cell proliferation.

HBV and HCV both cause liver disease that progresses through fibrosis and cirrhosis before cancer emerges. EBV establishes lifelong latent infection in the host’s B cells and epithelial cells; growing epidemiological and biological evidence links this persistent latency not only to cancer but to autoimmune conditions including multiple sclerosis.

Understanding these mechanisms points toward the interventions most likely to work: for HPV, vaccination before exposure; for H. pylori, population-level testing and eradication; for HBV and HCV, antiviral therapy in chronically infected individuals; for EBV, a preventive vaccine that does not yet exist but is being actively developed.

What this means for you

A finding that infections contribute to roughly 12% of cancers worldwide sounds alarming. But there’s another side to the IARC analysis: infection-related cancers offer some unusually direct opportunities for prevention.

Vaccines can prevent infection with HPV and hepatitis B. Cervical screening can identify HPV-related changes before they become cancer. Hepatitis C can now be cured in most people who receive modern antiviral treatment, while H. pylori can be detected and eradicated with appropriate treatment. EBV remains the major exception among the five, with no approved preventive vaccine currently available. Pasted markdown Pasted markdown

That doesn’t mean everyone needs to be tested for every infection on this list. Who should be vaccinated, screened, or tested depends on factors such as age, vaccination history, symptoms, previous screening, family history, and individual risk.

The global numbers also reveal how unevenly these opportunities are distributed. Three-quarters of infection-related cancers occurred in low- and middle-income countries, where access to vaccination, screening, diagnosis, and treatment can be more limited. Pasted markdown

For individuals, the practical takeaway is much simpler. Knowing your vaccination history, participating in recommended cancer screening, and discussing appropriate infection testing with a healthcare provider can address some of the risks identified in this research.

Cancer will never be entirely preventable. Genetics, aging, environmental exposures, lifestyle, and chance all play roles that are much harder to control.

But when cancer begins with an infection that can be prevented, detected, treated, or even cured, there is an opportunity to intervene years before a tumor ever appears.

Disclaimer: This information is not intended to be a substitute for professional medical advice, diagnosis, or treatment and is for information only. Always seek the advice of your physician or another qualified health provider with any questions about your medical condition and/or current medication. Do not disregard professional medical advice or delay seeking advice or treatment because of something you have read here.

AI Disclaimer: This article was created with the assistance of AI tools and reviewed by a human editor.