Oncology Update | Transmissible Venereal Tumours
Central Toronto Veterinary Referral Clinic
Transmissible venereal tumours (TVT) were typically rare in North America, Canada in particular. However, with the dramatically increased volume of dog rescue and adoption from endemic regions, I am seeing this tumour more than ever before.
TVT is a round cell or immune system cancer, which is horizontally transmitted typically by sexual activity. Transmission can occur easily in either direction between the dog and the bitch. TVT can also be transmitted by licking, sniffing and biting affected areas. As sexual activity is not the only mode of transmission, TVT can easily be transmitted within a household by a new dog, even if other dogs in the home are neutered or spayed. TVT is most commonly reported in Central and South America, the Caribbean, the southern USA and southeastern Europe. The incidence is highest in regions with large numbers of free roaming, sexually intact and sexually active dogs.
No breed or sex predilection has been noted. The most common age of onset is between 2 and 5 years. Lesions most commonly develop on the external genitalia. In the female, TVT will typically develop within the vaginal vestibule. In the male, lesions most commonly develop at the very base of the penis and retraction of the sheath is necessary in order to visualize the mass. Other locations for lesion development include the nasal and oral cavities, skin, eyes and perianal region.
TVT is typically a slow growing cancer with a very low metastatic rate, reported to be between 5% and 17%. TVT lesions have a very classic appearance. The tumour usually forms as a proliferative single mass or series of closely associated masses. The masses are nodular with a “cauliflower” appearance. They are usually frim but friable and are deep red in colour with surface ulceration noted. The mild oozing of blood is responsible for the most common clinical sign, bloody discharge from the vulva or penis sheath.
TVT is very easily diagnosed by cytology. This tumour exfoliates cells well. Evaluation of samples collected by fine needle aspirate or even by swab or by tumour impression imprints will generally yield a definitive diagnosis. Though not usually necessary, TVT can be diagnosed with histopathology. The use of biopsy is generally reserved for cases where cytology fails to offer a diagnosis.
TVT is a highly highly treatable cancer and in most cases is curable. Many forms of treatment have been described. These include chemotherapy, radiation therapy and surgery. Chemotherapy has been demonstrated to be the most effective therapy. Surgery is not typically recommended unless the lesions are small, discrete and able to be removed with adequate margins. Complete excision is difficult to achieve in most cases and residual disease will recur in up to 75% of cases.
Chemotherapy treatment is successful in curing TVT in 90%-95% of cases. Single agent therapy is applied and is given weekly. Treatments continue until there is complete remission of all lesions and then for 2 additional weeks. Signs of bleeding usually resolve after 1 or 2 treatments and tumour tissue is gone, most commonly, by the 4th treatment, after which 2 further treatments are given. Treatments are well tolerated with a very low incidence of side effects. TVT is a curable tumour with an excellent prognosis.
Dr. Kevin Finora is a Board Certified Oncologist and Small Animal Internist who is part of the Healthcare Team at the Central Toronto Veterinary Referral Clinic. He is available for referrals and consultations Monday to Thursday (including Monday and Tuesday evenings). Please contact him with any oncology questions or concerns.
Posted by: Michael Goldstein, DVM, Diplomate ACVIM
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