Canine transmissible venereal tumour: a new treatment route?
What is canine transmissible venereal tumour?
The immune system is known to play a part in tumour growth and metastasis, although metastases are very rare.
Clinical signs
Canine transmissible venereal tumour has two clinical presentations:
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Genital: in males, the tumour is located at the base of the penis, although it may also have other, less common locations. In females, TVT affects the vagina and/or vulva. It begins in a very small and hyperemic form which then grows like a lobed cauliflower with a very friable consistency.
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Extragenital: inside the nose, oral cavity (lips and tongue), eyes (sclera and anterior chamber of the eye) and skin.
Diagnosis of canine transmissible venereal tumour
The diagnosis is based on a physical exam, medical history review (sexual contact) and histopathology.
As vaginal secretions can contain neoplastic cells, exfoliative vaginal cytology is an easy and effective method of diagnosing and following up the recovery of TVT in females.
Although metastases are not common, it is important to examine regional lymph nodes and, if in doubt, a fine-needle aspiration should be performed to confirm whether or not they are affected.
Effectiveness of treatment with vincristine and interleukin-2
Transmissible venereal tumour can be approached with different treatments such as surgery, cryosurgery, radiotherapy and chemotherapy.
Surgical excision is sufficient for small tumours. If surgery alone is performed on larger tumours, there is a 60% chance of local recurrence. In these cases, vincristine should be administered intravenously every week for up to 2 weeks after achieving clinical cure. The method is very effective and has a 90% success rate.
Several studies have been conducted recently to test the efficacy of treatment with vincristine and interleukin-2. In a study of females with vaginal tumours, the subjects were treated weekly for 3 to 6 weeks, and the tumours progressively decreased in size until they had completely disappeared. Side effects involved vomiting, diarrhoea and neutropaenia. All subjects underwent a physical exam and vaginal smear one year after treatment, and no abnormal cells were observed in any of the cases.1
Similar results were observed in a study in male dogs that were also treated with interleukin-2 (IL-2).2
Thus, vincristine and IL-2 have been confirmed as effective intratumoral treatments in TVT.
Doxorubicin can be used if vincristine does not produce a response.
Prognosis
The prognosis is usually good, with or without chemotherapy treatment. Although it can be described as a malignant tumour, it does not usually behave as such and metastases are rare.
