Infectious dog cancer is spreading in the UK again: Cambridge offers vets a free test — what we know about canine transmissible venereal tumour

What has happened

The University of Cambridge has appealed to UK vets: its veterinary school, through the Transmissible Cancer Group, is asking them to report all suspected cases of canine transmissible venereal tumour, or CTVT. Vet Times reported on the appeal on 27 October 2026.

The reason is a rise in cases. A recent clinical case report confirmed that the tumour is once again actively passing between dogs within the UK. According to Vet Times, it's the first such confirmed case in 50 years. The rise is thought to be linked to importing dogs from regions where the disease is still widespread, particularly Eastern Europe.

What Cambridge is offering

The Cambridge group has launched a pilot study. UK vets can send a sample of a suspicious tumour free of charge, and the laboratory will test it by PCR, using DNA found only in the cells of this tumour. The researchers promise definitive results within a "clinically useful" timeframe — in other words, fast enough for the vet to make treatment decisions.

Participation will directly advance the understanding of CTVT transmission in the UK.

Andrea Strakova, postdoctoral scientist at the University of Cambridge

Samples for DNA extraction can be submitted in any form. The preferred submission is a frozen tumour biopsy at least the size of a larger pea, or a pea-sized biopsy in formalin.

What the disease is

Canine transmissible venereal tumour is one of the few known infectious cancers in nature. Ordinary cancer arises from an animal's own cells and can't be passed on. CTVT is different: the tumour cells themselves move from one dog to another and take hold in the new host. All such tumours worldwide are descended from the cells of a single dog that lived several thousand years ago. Since then the clone has spread to every continent.

The tumour is passed on mainly during mating, so it most often grows on the genitals. Less often, the cells reach the nose, mouth, skin or the area around the eyes — when dogs sniff and lick each other.

What it looks like

Vet Times lists signs that should make vets think of CTVT, especially in dogs that have travelled from areas where the disease is common:

• bloody discharge from the genitals — from the prepuce in males and the vulva in females;
• nodular masses on the genitals that bleed easily and crumble when touched.

Less often the tumour appears on the nose (causing nosebleeds and sneezing), in the mouth or on the skin. It can look like a cauliflower, sometimes ulcerates and may smell unpleasant. Owners often mistake bloody discharge in a bitch for a season, and in a male dog for an injury or infection.

Why vets might not recognise it

Researchers fear that many UK vets simply won't recognise this tumour: it has hardly been seen in the country for decades. Without suspicion of CTVT, the masses may be taken for other tumours or inflammation, and the dog treated for the wrong thing for a long time. That's exactly why Cambridge is offering a free test: it helps with an accurate diagnosis and at the same time shows researchers how widely the tumour has spread.

The link with imported dogs

In the UK and other countries of northern and western Europe, CTVT almost disappeared as stray dog numbers fell and most pet dogs were neutered or kept under control. But in countries with many free-roaming dogs that mate freely on the streets, the disease is still common — in southern and eastern Europe, Asia, Africa and Latin America.

In recent years many dogs from shelters and streets in these regions have been brought to the UK and other European countries. Most are healthy, but some may carry a tumour that isn't yet visible. If such a dog isn't neutered and mates with local dogs, the tumour starts to spread — which, judging by the case report, is what has happened.

How it's diagnosed

Faced with a suspicious mass, a vet usually first takes cells with a fine needle or makes an impression smear and looks at them under the microscope. CTVT cells are fairly distinctive: round, with clear vacuoles inside, and an experienced cytologist often recognises them straight away. But similar cells occur in other tumours, such as lymphoma or mast cell tumours. So a DNA test helps confirm the diagnosis: CTVT cells have genetic features that the dog's own cells lack. That's exactly the kind of test the Cambridge laboratory is offering.

An accurate diagnosis matters not just for treatment. It helps establish where the tumour came from and allows other dogs that may have been in contact with the affected dog to be checked.

How widespread the tumour is worldwide

CTVT occurs on every inhabited continent. Most cases are found where there are many stray and free-roaming dogs — in parts of Asia, Africa, Latin America and southern and eastern Europe. Cambridge researchers have spent years collecting samples of this tumour from around the world and using its DNA to reconstruct how it travelled with people and their dogs. For scientists, CTVT is a unique model: it helps reveal how cancer can evade the immune system of another body.

The good news: it's treatable

According to Vet Times, CTVT is considered highly treatable once diagnosed: the tumour usually responds to chemotherapy with vincristine. Treatment involves several doses given at intervals, and in most dogs the tumour disappears completely. The protocol and dose are decided only by a veterinary oncologist or the treating vet: the drug is toxic and requires blood monitoring.

In the rare cases where chemotherapy doesn't work, other approaches are used. Surgery alone often fails: the tumour comes back if any of its cells are left in the wound.

What owners of rescue dogs from abroad should know

If your dog came from a country with many stray dogs, there's no need to worry — but it's worth being alert:

1. Check your dog's genitals during routine grooming for lumps, discharge or bleeding.
2. Don't mistake discharge for a season. If your bitch has bloody discharge outside her season, or for too long, take her to the vet.
3. Tell your vet where your dog came from: it helps them think of diseases that are rare in the UK.
4. Discuss neutering — it protects against CTVT and many other problems.
5. Prevent accidental matings until you're sure your dog is healthy.

What rescue organisations should know

Organisations that bring dogs from abroad can reduce the risk by having each dog examined by a vet before travel and after arrival, and tested if there are suspicious masses. Neutering before rehoming adds further protection. The Cambridge project is a good opportunity to check uncertain cases free of charge and to work with researchers to understand how big the problem is.

What happens after arrival matters too. New owners often don't know what to look for, so rescues should tell them about the signs of CTVT and other diseases that are rare in the UK: that bloody discharge in a dog is a reason to see a vet, not to wait for it to "clear up on its own". A short information sheet given at rehoming can save months of incorrect treatment.

What this means for the rest of Europe

The issue isn't confined to the UK. Many dogs from regions where the tumour is common are also brought into EU countries, and vets in northern and western Europe rarely see it — so they may not recognise it either. The UK example shows that even a disease that had long "disappeared" can return with the movement of animals. Vets in Germany, France, Scandinavia and elsewhere should bear CTVT in mind when a dog arrives with bloody discharge and masses on the genitals, especially if it was imported.

Is it dangerous to people or cats

No. CTVT passes only between dogs and other members of the dog family. People, cats and other pets can't catch it. Even so, it's sensible to wear gloves and wash your hands when caring for a dog with a bleeding tumour — simply for hygiene.

When to see a vet

Take your dog to the vet if they develop bloody discharge from the genitals, lumps or growths there, nosebleeds, an unpleasant smell or any new growths on the skin or mucous membranes. Don't delay, especially if your dog was imported from another country or may have had contact with such dogs. The earlier the diagnosis, the simpler and shorter the treatment.