Transmissible Venereal Tumour

These notes are provided to help you understand the diagnosis or possible diagnosis of cancer in your pet. For general information on cancer in pets ask for our handout “What is Cancer”. If not already performed your veterinarian may suggest certain tests to help confirm or eliminate the diagnosis, and to help assess treatment options and likely outcomes. Because individual situations and responses vary, and because cancers often behave unpredictably, science can only give us a guide. However information and understanding of tumours in animals is improving all the time.

We understand that this can be a very worrying time and we apologise for the need to use some technical language. If you do not understand anything, please do not hesitate to ask.

What is this tumour?

This is a common tumour, only found in dogs. It has a patchy world-wide distribution including parts of the Caribbean, USA, Southern Europe, Asia and Africa. It has not been officially recorded in Australia. It is transmitted by physical transplantation. It occurs in both sexes and may appear as multiple subcutaneous nodules on the genitalia, lips and other parts of the body.

What do we know about the cause?

The reason why a particular pet may develop this, or any cancer, is not straightforward. Cancer is often seemingly the culmination of a series of circumstances which come together for the unfortunate individual.

The tumour is a transplant of cancer cells. The cancer cells always have an abnormal number of chromosomes (59 instead of the normal canine 78). The original cell type is probably a histiocyte (part of the body’s own immune system) but other types of white blood cell have also been suggested as the origin.

Why has my animal developed this cancer?

The cancer is transmitted by sexual contact or direct contact with the infected tumour (e.g. by licking).

Is this a common tumour?

These are common tumours of dogs in some parts of the world, particularly in stray dogs.

How will this cancer affect my pet?

The tumours are nodules, sometimes multilobulated, often on the penis or vulva. Most ulcerate and bleed. The cancers may spread through the body with many tumours in the skin.

The tumours grow rapidly at first and then remain static for a time. Eventually, they spontaneously regress due to antibody production by the immune system.

How is this cancer diagnosed?

Clinically, this tumour has a fairly typical appearance. Definitive diagnosis relies upon microscopic examination of tissue.

Various degrees of surgical sampling may be needed such as needle aspiration, punch biopsy and full excision. Cytology is the microscopic examination of cell samples. This is used for rapid or preliminary tests and can be diagnostic for these tumours. The most accurate diagnosis, prediction of behaviour (prognosis) and a microscopic assessment of whether the tumour has been fully removed rely on microscopic examination of tissue (histopathology). This is done at a specialised laboratory by a veterinary pathologist. The piece of tissue may be a small part of the mass (biopsy) or the whole lump but only examination of the whole lump will indicate whether the cancer has been fully removed. Histopathology also rules out other cancers.

What types of treatment are available?

The commonest treatment is surgical removal of the lump. Other treatments include chemotherapy and radiation. These are not suitable for all types of cancer and often have significant side effects. Some are only available at specialist centres.

Can this cancer disappear without treatment?

Yes. This cancer grows rapidly at first and then remains static before the dog’s immune system produces specific antibodies that cause the tumour to spontaneously regress. That dog is then highly resistant to further tumour implantation.

How can I nurse my pet?

Preventing your pet from rubbing, scratching, licking or biting tumours will reduce itching, inflammation, ulceration, infection and bleeding. Any ulcerated area needs to be kept clean.

After surgery, the operation site similarly needs to be kept clean and your pet should not be allowed to interfere with the site. Any loss of sutures or significant swelling or bleeding should be reported to your veterinarian. If you require additional advice on post-surgical care, please ask.

How will I know if the cancer is permanently cured?

“Cure” has to be a guarded term in dealing with any cancer.

Histopathology will give your veterinarian the specific diagnosis that indicates how it is likely to behave. In healthy dogs, spontaneous regression will indicate full cure and the tumour is unlikely to regrow.

Are there any risks to my family or other pets?

This is a tumour that can be transmitted from dog to dog. Preventing physical contact between your infected dog and others is essential. You should also wash your hands after handling your dog and disinfect anything that may be contaminated with living cells from your dog and then come into contact with other dogs. The tumour cannot be transmitted from dogs to other species or to people.