Canine Trasmissible Veneral Tumor Vaginal with Ocular Metastasis - Therapeutic Decision Based on Ocular Ultrasound

Background: Canine transmissible venereal tumor (cTVT) is a contagious round cell tumor that can occur in ocular structures primarily and by metastasis. The objective of the present study is to report a case of vaginal cTVT with ocular metastasis that was based on the findings of ocular ultrasonography as the basis for the therapeutic decision. Case: A 2-year-and-9-month-old bitch without a defined breed (MBD), weighing 17 kg, complaining of a mass in her left eye which had been developing for 3 months, was presented for clinical care. It was reported that the animal had initially had a fight with a cat and presented with blepharospasm, opacity and an eyelid wound, evolving after 1 month to the mass reported. There was also an increase in volume in the vulva with a discreet bloody secretion, which was already present before the fight with the cat.  On general physical examination, the vulvar and ocular masses were similar, being exophytic, reddish, friable, amorphous, ulcerated, alopecic and bleeding easily. No alterations were found in the search for metastases using chest X-rays, total abdominal ultrasound and fine needle puncture cytology of the inguinal and submandibular lymph nodes. Swab cytology and vaginal imprinting were carried out, which consisted of many round cells arranged in isolation.  An imprint was also made of the eye lesion, which consisted of intense amounts of inflammatory cells with a predominance of degenerated neutrophils and moderate number of isolated round cells. It is therefore a plasmacytoid subtype of cTVT. The patient underwent an ocular ultrasound of the left eye, which was enlarged. The internal architecture was altered by the presence of a heterogeneous, irregular mass measuring 2.4 x 2.2cm, occupying more than 50% of the eyeball, including the region of the iridocorneal angle, extending to near the retina. Based on the clinical findings and complementary exams, exenteration of the left eye was recommended, followed by complementary chemotherapy with vincristine sulphate at the maximum tolerated dose. Histopathological examination of the eyeball showed a densely cellular, non-encapsulated tumor mass composed of rounded cells arranged in a mantle and supported by moderate fibrovascular stroma and marked marginal neovascularization. The biopsy concluded that the diagnosis was round cell neoplasia, with cTVT being probable, immunohistochemistry was requested for a confirmatory diagnosis but was not authorized by the owner due to the cost.  Therefore, the final diagnosis of the case was defined based on the anamnesis, macroscopic tumor characteristics, ocular ultrasound and cytology as vaginal cTVT with ocular metastasis. The owner did not return with the animal to carry out the chemotherapy. Discussion: This report corroborates the already known profile of animals affected by cTVT in Brazil, as the patient was not neutered and had access to the street, even having interbred with stray animals. Ocular involvement by cTVT is considered uncommon and can make diagnosis more challenging, as it can be confused with other pathologies. Studies detailing clinical decision-making based on ocular ultrasound evidence are scarce in the literature. Therefore, ocular ultrasound can be a key factor in the decision to treat with chemotherapy or enucleation, as it can highlight the structures affected by the mass. Vincristine treatment appears to be most effective when internal structures are not involved. In this case, it was assumed that chemotherapy alone would likely not be effective, and therefore, exenteration was indicated. Ocular ultrasound evaluation can guide the decision-making process between medical and surgical treatment of ocular cTVT, but further studies evaluating the efficacy of this test are still needed. Keywords: cancer, dog, eye, neoplasia.