Fifteen to twenty percent of all human cancers are caused by viruses, such as the hepatitis B virus. Cats naturally catch similar viruses. Veterinarian Julia Beatty and molecular biologist Thomas Tu argue that the felines could become a very interesting model for studying these cancer-causing viruses, helping researchers develop treatments and prevention strategies that benefit pets and people alike.
Key messages:
- Viruses cause roughly one in five human cancers worldwide, including some liver cancer (hepatitis B and C), cervical cancer (HPV), and leukemia (HTLV-1), according to the International Agency for Research on Cancer.
- Cats naturally catch close relatives of several human cancer-causing viruses – including versions of hepatitis B, HIV, and papillomaviruses – making them one of the few animals that can model virus-driven cancer without artificial infection.
- The 1967 discovery of feline leukemia virus (FeLV) by veterinarian William Jarrett was the first proof that ordinary mammals – not just lab animals – could naturally develop cancer from a virus, a finding that later helped researcher Robert Gallo identify the human cancer-causing retrovirus, HTLV-1.
- No animal model can fully replicate how the hepatitis B virus (HBV) causes liver cancer in humans – mice aren't naturally susceptible to HBV, but cats infected with a related virus (DCHBV) may fill that gap.
- Researchers Julia Beatty and Thomas Tu (2026, Nature Reviews Cancer) are calling for an international consortium to study naturally occurring feline cancer viruses, arguing pet cats could accelerate cancer research for both veterinary and human medicine.
Viruses can cause cancer
Viruses that cause cancer are called oncoviruses. Most viruses infect only one type of cell – the viruses behind the common cold, for instance, infect just the cells lining your nose and throat. But sometimes a virus changes the cells it infects in a way that makes them turn cancerous.
The first evidence of these viruses came in 1910, when physician Peyton Rous studied tumors in chickens. In landmark experiments, he took cells from a tumor, filtered them to keep anything smaller than a cell, and injected the filtrate into healthy chickens, which then developed the same kind of tumor. This showed that something small enough to pass through the filter – later identified as a virus, now called the Rous sarcoma virus – could cause cancer. Rous won the Nobel Prize for the discovery in 1966.
Since then, researchers have identified several viruses that cause cancer in humans. Together, the International Agency for Research on Cancer estimates they're responsible for aournd one in five cancer cases worldwide. They include:
- The Epstein-Barr virus (EBV) – a herpes virus that’s spread through saliva
- The Hepatitis B virus (HBV) – the leading cause of liver cancer for which a vaccine exists
- The Hepatitis C virus (HCV) – also a leading cause of liver cancer, and linked to a blood cancer called non-Hodgkin lymphoma. There's no vaccine, but it's treatable
- The human papillomavirus (HPV) – at least 12 strains cause several types of cancers in men and women. A vaccine exists.
- Human T cell leukaemia virus-1 (HTLV-1) – which causes acute T cell leukaemia
- Human immunodeficient virus (HIV) – by suppressing the immune system, HIV contributes indirectly to the development of cancers.
Oncoviruses have been central to modern cancer research and provide profound insights into both infection-driven and non-infectious cancers.
Understanding cat viruses shaped modern oncology
Humans are not the only animals to be vulnerable to cancer-causing viruses. In fact, many human oncoviruses have turned out to have equivalents in cats. In a recent scientific publication in Nature, veterinarian Julia Beatty and molecular biologist Thomas Tu show how cats have been and will continue to be tremendously useful as a model to study these viruses, to better understand, prevent and treat them in both species.
Human and feline leukaemia-causing viruses
Feline viruses were first recognised as useful for cancer research about 60 years ago. In 1967, veterinarian William Jarrett, at the University of Glasgow, discovered that feline leukemia virus (FeLV) caused clusters of lymphoma and leukemia in cats living in the same household. In the 1960s and 70s, FeLV was estimated to cause 60%–70% of all feline lymphoma and leukemia cases. Numbers declined to less than 15% by the early 2000s, after a vaccine became available for cats. Similar cancer-causing viruses had already been found in chickens and lab mice, but those discoveries were dismissed as biological curiosities with little to no relevance to people.
The discovery of FeLV changed that. It was the first proof that ordinary mammals, not just lab animals, could naturally develop cancer because of a virus. That insight pushed clinician Robert Gallo to start looking for a viral cause of human leukemia. His team began by studying feline and other animal viruses to understand how they turned cells cancerous – work that eventually led them to identify the human T-cell leukemia virus-1 (HTLV-1), the cause of acute T-cell leukemia in people.
The human (HIV) and feline (FIV) immunodeficient virus
Feline immunodeficiency virus (FIV), is a relative of HIV discovered in 1987, at the height of the AIDS epidemic. Unlike untreated HIV, which progresses to AIDS, FIV usually causes a milder, often symptom-free form of immune suppression in cats. Still, it raises their risk of developing lymphomas that closely resemble those seen in people with AIDS.
In humans, HIV doesn't cause cancer directly. Instead, it weakens the immune system, which lets other cancer-causing viruses, such as a family called gammaherpesviruses (GHVs), do more damage. Comparing FIV in cats to HIV in humans, researchers concluded that both viruses promote cancer in the same indirect way, leading to the discovery of a feline version of GHVs (FcaGHV1). Cats with FIV could become an important model for understanding the link between immune suppression and cancer-causing viruses.
Papillomaviruses
Several hundred species or types of papillomaviruses have been identified in mammals but also other vertebrates such as birds, snakes and other reptiles, turtles and fish. Papillomaviruses are rarely transmitted between species but they represent an opportunity to understand the human viruses, including how and why some may cause cancers. The feline papillomaviruses (FcaPVs) cause several types of cancers and share oncogenic actions with HPVs. As such the comparative value of these feline viruses is of particular interest, especially in cutaneous squamous cell carcinomas (SCC). As some cat breeds are at a heightened risk of developing the cancers linked to FcaPV infection, a feline model may help map the genetic susceptibility that influences host vulnerability to papillomaviruses.
Feline papillomaviruses (FcaPVs) cause several types of cancer in cats and share cancer-causing mechanisms with human papillomaviruses (HPVs). As such the comparative value of these feline viruses is of particular interest, especially squamous cell carcinomas, a type of skin cancer. Because some cat breeds are especially prone to FcaPV-linked cancers, studying them could also help identify the genes that make some individuals — cat or human — more vulnerable to papillomavirus-driven cancer.
The hepatitis B virus and its feline equivalent
Hepatitis B virus (HBV) infection is the leading cause of hepatocellular carcinoma (HCC) – a common form of liver cancer – in people. A similar virus can be found in cats (called DCHBV), which shares much of the same genomic structure as HBV. Studies comparing the two suggest that liver cancer develops through similar processes in cats and people.
Until now, no animal model had fully captured how HBV leads to cancer. Mice aren't naturally susceptible to HBV, and genetically engineered mouse models are limited to viral tolerance and minimal liver disease. Other animals that can be experimentally infected with HBV-like viruses don't develop cancer the way people do. But recent studies suggest that cats may fill that gap. The felines could offer real insight into HBV-linked liver cancer, benefiting both human and veterinary patients.
Cat viruses as windows into human oncogenesis
Beatty and Tu's paper argues for the importance of pet cats - naturally infected with viruses and living alongside their families - in future cancer research, and calls for an international consortium to develop a framework of governance and to standardise how data on feline cancer viruses is collected and shared worldwide. Studying infections that already occur naturally in pet cats could help researchers pinpoint the molecular drivers of cancer and spot similarities between viruses in cats and people.
Because cats are genetically diverse, live alongside their humans and are in contact with much of the same environement, they could be valuable not just for basic lab research, but for studies that are hard to run in a lab at all. For example, researchers could compare cancer rates between cats in smoking and non-smoking households to study how tobacco smoke – a known cancer risk factor in humans – interacts with viral infection. More research is needed to confirm exactly how closely feline and human biological drivers for cancer line up, but studying cats this way could add another layer of understanding to problems that are hard to solve in the laboratory alone.
Cats also stand to benefit directly: vaccines and treatments developed for human viruses, including HBV, could potentially be adapted for use in cats. This kind of two-way exchange between veterinary and human medicine, known as comparative oncology, already has a good track record. Studies of pet dogs with naturally occurring cancers have demonstrated the power of companion animal models to speed up the journey from lab discovery to human clinical trials.
Pet dogs with cancer have catalysed the translation of preclinical discoveries to first-in-human trials, highlighting the unique power of comparative oncology to study veterinary and human patients with cancer in parallel. Naturally occurring cancers in pet dogs are considered one of the most useful real-world settings in which to study cancer for human benefit, because they (1) develop in animals with an intact immune system and are genetically diverse, (2) they genetically and phenotypically resemble human tumors, (3) they arise in the same environments humans live in, and (4) they respond to many of the same treatments used in people. Even so, the full mutual benefit of studying dogs and humans in parallel has yet to be fully realised.
Cats have received far less research attention than dogs, despite having the advantage (from a research point of view) that, unlike dogs, they are naturally susceptible to homologues of several human cancer-causing viruses. With potential benefits for both pets and people, the case for studying feline viral cancers is strong. As the researchers announce, it's a dormant resource, that's still largely untapped.
Main source : Beatty, J.A., Tu, T. Cat viruses as windows into human oncogenesis. Nat Rev Cancer 26, 233–235 (2026). https://doi.org/10.1038/s41568-026-00909-z
Frequently asked questions
What percentage of human cancers are caused by viruses?
Viruses are estimated to cause about 15–20% of human cancers worldwide, including cancers linked to the hepatitis B and hepatitis C viruses, HPV, Epstein-Barr virus, and HTLV-1.
Why are cats useful for studying cancer-causing viruses?
Cats naturally catch close relatives of several human cancer-causing viruses — including versions of the hepatitis B virus, HIV, and papillomaviruses — so studying these infections in pet cats can reveal how similar viruses cause cancer in people, without needing artificial lab infections.
What is feline leukemia virus (FeLV), and why does it matter for human cancer research?
FeLV is a virus that causes lymphoma and leukemia in cats. Its discovery in 1967 by veterinarian William Jarrett was the first proof that ordinary mammals could naturally develop cancer from a virus, a finding that helped inspire the research that later identified HTLV-1, a human cancer-causing retrovirus.
Is there a cat version of hepatitis B?
Yes. Cats can be infected with DCHBV, a virus closely related to the human hepatitis B virus (HBV) that shares a similar genomic structure and appears to cause liver cancer through similar mechanisms. Because no other animal model fully captures how HBV causes cancer in humans, cats may help close that research gap.
What are researchers proposing for the future of feline cancer virus research?
In a 2026 paper in Nature Reviews Cancer, veterinarian Julia Beatty and molecular biologist Thomas Tu call for an international consortium to standardize how data on feline cancer viruses is collected and shared, arguing that studying pet cats could accelerate cancer research for both veterinary and human medicine.
Last edited: 8 September 2026 11:24
