The transmissible venereal tumor (TVT) has been described since 1876 and is commonly found on both male and female dogs. Transmission is by simple physical contact between an existing tumor on one dog and abraded (irritated) skin 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 affect noses, mouths, anal areas, and other anatomical sites.
The transmissible venereal tumor may be visible as an external fleshy growth or may simply appear as genital bleeding (eventually the tumor will become eroded on the surface). 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. Because there is potential for tumor spread within the body, treatment is recommended to shrink the tumor rather than simply waiting it out.
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 that 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. Developing a TVT might analogous to getting bitten by a mosquito and the few mosquito cells left behind try to grow a new mosquito on the host’s body.
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). The tumor is classified as a round cell tumor and is related to more malignant round cell tumors such as the mast cell tumor and lymphoma.
There are several treatment options for the transmissible venereal tumor which include surgery, vincristine (the chemo injection Japser received) and radiation. Follow-up treatment with routine check-ups will be necessary and your family veterinarian will discuss these and other treatment options with you.