TRANSMISSIBLE VENERAL TUMOR
Imagine a tumor that can be transmitted by touch. For dogs, this is not a matter of imagination; the Transmissible Venereal Tumor has been described since 1876 and is not unusual where stray dogs roam free and have contact with one another. The tumor is found in both male and female dogs. Transmission is by simple physical contact between an existing tumor on one dog and abraded mucous membrane (oral, genital, nasal etc.) on another. It is most commonly spread during mating but can also be spread during routine sniffing or other contact. In most cases, tumor growth is found on the genitals but it can also just as easily emerge on noses, mouths, anal areas, and other anatomical sites.
The Transmissible Venereal Tumor, affectionately known as the TVT, may be visible as an external fleshy growth or may simply present as genital bleeding (eventually the tumor will become eroded on the surface and bleed). As mentioned, the tumor is common where there are large numbers of roaming dogs or in shelter situations. In most cases the tumor is not malignant and simply grows and bleeds at a local site eventually being rejected by the patient’s immune system; however, resolution of the tumor can take over 9 months which is a long time for a patient to bear a bloody infected growth. In approximately 10% of patients, the tumor actually does spread malignantly in a cancerous fashion though this is more likely in dogs that have an immunological compromise (young age, poor general health, concurrent other disease). Because of the long time to resolve and the potential for spread, treatment is generally recommended over simply allowing the tumor to regress.
Strangely, the tumor cells are not the patient’s own cells transformed into cancer cells. This is not a matter of a virus being transmitted which causes normal cells to become cancerous. The TVT is actually a tumor that grafts itself from one dog's body onto another dog's body. Unlike the host's normal cells, TVT cells have a completely different number of chromosomes and do not originate from the host at all. Developing a TVT might analogous to getting bitten by a mosquito and the few mosquito cells left behind actually trying to grow a new mosquito on one’s body.
In this cell sample, the small round cells are red blood cells. The large blue-purple cells are TVT cells.
Diagnosis is made either by biopsy (taking a small piece of tumor tissue for analysis) or by cytology (obtaining a smear of the tumor’s cells and looking at it under a microscope as shown above). The tumor is classified as a “Round Cell Tumor” and is related to more malignant Round Cell Tumor such as the Mast Cell Tumor and Lymphoma.
Treatment of the Transmissible Venereal Tumor is straightforward and generally very rewarding:
Page last updated: 6/14/2019