THE PET HEALTH LIBRARY By Wendy C. Brooks, DVM, DipABVP Educational Director, VeterinaryPartner.com

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 commonly found on both male and female dogs.

Transmission is by simple physical contact with the tumor and is most commonly spread during mating but can also be spread during routine sniffing or other contact. Most of the tumor the growth is found on genitals but can also be 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 appear as genital bleeding (eventually the tumor will become eroded on the surface). 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, if the patient is immune-suppressed due to young age or poor general health, then the tumor can spread in a cancerous fashion. Strangely, the tumor cells are not the patient’s own cells transformed into cancer cells; tumor cells have their own number of chromosomes. Developing a TVT might be analogous to getting bitten by a mosquito and the few mosquito cells left behind actually trying to grow a new mosquito on the 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 tumors such as the mast cell tumor and lymphoma.

Treatment

Treatment of the transmissible venereal tumor is straightforward and generally quite 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 venereal tumor, one of the other treatment methods should ensue.
   
  • Vincristine
  Vincristine is a chemotherapy agent that must be delivered intravenously. Certain IV catheters or butterfly units are placed to deliver the drug, as any spillage 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 or two treatments but generally 3 to 6 weekly treatments are administered to ensure a cure.
   
  • Radiation
  External beam radiation is effective in curing the TVT but is expensive and not readily available. If you are near a facility, however, this may be a good option.

Fanny Mae looks to be about 10 years old and lives behind the Thong Sala market in Thailand. Her sweet nature has managed to earn her enough food to survive this long, but the tumor growing from her vagina would eventually take her life if left untreated.

These pictures indicate decrease in mass after only two treatments of vincristine.

See a more complete history of Fannie Mae from the PhaNgan Animal Care, Koh PhaNgan Suksa School.

Date Published: 3/27/2004 7:28:00 PM
Date Reviewed/Revised: 07/25/2008