Canine Transmissible Venereal Tumor in the Larynx with Pulmonary Metastasis

Abstract

Background: Canine transmissible venereal tumor (TVT) is one of the most common canine neoplasms in Brazil. Lesions develop mainly in the genital tissue and less frequently in other areas, in the extragenital form. Metastasis is rare, and the disease progression depends on the patient’s immune status. The treatment of choice is chemotherapy with vincristine sulfate, considered an effective and safe modality. The present work describes the first case of extragenital TVT in the larynx with pulmonary metastasis at the time of diagnosis. Case: An approximately 4-month-old mixed-breed bitch was attended manifesting acute clinical respiratory signs. The patient had been rescued from the street 2 months beforehand. Physical examination revealed pale mucous membranes and crackling pulmonary auscultation. Thoracic radiography was performed in 3 projections, showing multiple nodules in the lung parenchyma, followed by cytopathological examination using fine needle puncture guided by thoracic ultrasound, confirming the diagnosis of TVT. Considering the cytological finding and the absence of primary tumor lesions in the genital, oral, cutaneous or nasal regions, endoscopy was performed in order to locate a possible primary focus. The exam revealed a small erythematous tumor with smooth and regular surface, measuring approximately 2.5 cm, located in the larynx, between the arytenoid cartilages. Chemotherapy was performed with vincristine sulfate with radiographic follow-up throughout the treatment. Full remission of the pulmonary and laryngeal nodules was achieved at the end of the protocol. The animal remained in complete remission for a period of 2 years. Discussion: TVT is more frequently observed in animals of active reproductive age, and rarely in animals under 1 year of age, as in the case described here. When considering extragenital lesions, the manifestation can be single or multiple, occurring more frequently in the cutaneous, oral and nasal forms. This case describes a laryngeal lesion with pulmonary involvement, without lesion in the genitalia or any other site. Cases of TVT in young and prepubescent animals, associated with extragenital involvement and aggressive behavior, similar to this case, have been described in literature, but never in this location. Literature suggests there is a relationship with the immune status of such patients, which do not have a well-developed immune system, facilitating disease progression. In these animals, transmission can be maternal, since in some cases the patient develops the disease without having contact with other animals except the mother. This form of transmission would facilitate the extragenital form in the oral cavity, airways and ocular region, related to licking, lactation and direct contact. Vincristine sulfate chemotherapy, considered the treatment of choice, was effectively used in this case, despite the atypical form. The TVT prognosis tends to be favorable, with the exception of the aggressive presentations with the presence of distant metastases. However, in the case described here, even though metastatic pulmonary nodules were present, complete remission was achieved, with survival exceeding 2 years. The development of TVT in the larynx is a rare form of the disease, and this report is possibly the first description of this tumor location. Thus, we highlight the importance of a complete investigation of the patient and of TVT as a differential diagnosis in this location.