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.

(Photocredit: Morguefile)

The Transmissible Venereal Tumor, also more succinctly called 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.
(Photocredit: Joel Mills via Wikimedia Commons)

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 TVT is one of several tumors classified as a "Round Cell Tumor." Biopsy samples are more accurate whereas a smear exam might only indicate that the growth in question is a Round Cell Tumor without being more specific.

TREATMENT

Treatment of the Transmissible Venereal Tumor is straightforward and generally very rewarding:

• SURGERY:
  Surgery is not as effective as one would expect. In one study of 70 dogs, 22% had recurrence within 5 months. If a tumor is surgically removed and found to be a Transmissible Veneral Tumor, one of the other treatment methods should ensue.
• VINCRISTINE:
  Vincristine is a chemotherapy agent which must be delivered intravenously. Special IV catheters or butterfly units are placed to deliver the drug as any spillage of the drug into the tissue surrounding the vein results in a painful tissue slough (i.e. a chemical burn occurs). This, however, is the only serious risk in this treatment and as long as proper IV materials are used this complication is rare. The TVT responds after only one treatment or two but generally 3-6 weekly treatments are administered to ensure a cure. There is some evidence that the treatment course is shortened when an appropriate canine non-steroidal anti-inflammatory medication is added into the regimen.
  
• DOXORUBICIN:
  Doxorubicin, also called Adriamycin, is another chemotherapy agent that must be given intravenously. It is a bit more intensive in its chemotherapeutic properties compared to vincristine but if vincristine is ineffective or yields only partial results, doxorubicin may be used to complete therapy.
• RADIATION:
  External beam radiation is very effective in curing the TVT but is very expensive and not readily available. If one is near a facility, however, this may be a good option.

Page last updated: 8/5/2023