Acta Scientiae Veterinariae, 2016. 44(Suppl 1): 142
Canine transmissible venereal tumor (TVT) is a round-cell tumor of dogs, which occurs by cell transplantation. It is usually located on the external genitalia, and is transmitted by coitus. It may occasionally be acquired by sniffing or licking the genitalia of an affected animal. Lesions may be present in the other parts of the body, such as the skin, rectum, and nasal or oral cavities. Metastasis of the TVT is uncommon, mainly occurring in immunocompromised dogs. It may affect organs such as the liver, spleen, kidney, lung, and musculature, and rarely, may be detected in the central nervous system. In this report, we describe the occurrence of a TVT causing spinal cord compression in a dog, and the results of its treatment with hemilaminectomy and chemotherapy.
A six-year-old male Dalmatian dog was referred to a veterinary teaching hospital with nonspecific abdominal pain. Laboratory examination showed no abnormalities; survey radiography revealed a moderate fecal retention. The dog received painkillers and dietary guidelines. However, the patient was brought again to the veterinary teaching hospital nine days later with paraplegia, worse in the left limb than in the right, but with normal nociception. There was a cutaneous trunci reflex cut-off at the T10 vertebra, also worse on left side than on right, along with spinal thoracolumbar hyperesthesia. During endotracheal intubation for general anesthesia for performing a cerebrospinal fluid tap and myelography, a small mass was observed in the palatine tonsil, a sample of which was collected for cytological analysis. The cerebrospinal fluid examination showed albuminocytologic dissociation, and myelography revealed an asymmetrical epidural compression over the T8 vertebra. Surgery was performed with a lateral approach to the T8 vertebra, and a 3-cm epidural brown mass was found, which was completely excised and subjected to histopathological examination. The histopathological findings of the mass excised from the spine revealed neoplastic proliferation of poorly differentiated, round tumor cells with large, round, central or peripheral nuclei, and slightly eosinophilic, occasionally vacuolar cytoplasm. The propagating cells formed groups separated by a delicate fibrovascular stroma, consistent with the histopathology of TVT. Upon immunohistochemical staining, the neoplastic cells were found to be positive for MHC II, CD45RA, and lysozyme, but negative for cytokeratin, CD3, CD20, and CD117. The cytological examination of the tonsillar mass confirmed TVT. The dog was treated with vincristine, but after the third cycle the treatment was discontinued due to the choice of the owner. A year after the treatment, the dog presents only a mild spinal ataxia.
Tumor cells can be transmitted through genital mucous membrane-contact at coitus. Hence, the TVT lesions are often located on the external genitalia, but this was not observed in this case. Non-cutaneous metastases, which have an incidence of about 1%, can occur on the lips and tonsils, as was observed in the present case, or in the inguinal lymph nodes, liver, kidneys, mesentery, bones, eye, brain, and abdominal cavity. The pathological characteristics of TVT is quite variable and depends on the host immune response; however, there was no evidence of immunosuppression or malnutrition in the present case. The patient might have acquired the neoplasia in the oral cavity probably from licking or sniffing the preputial or vaginal discharges of an infected dog, and therefore, the primary tumor was probably the one in the tonsil, which later metastasized to the spine. This case presents an atypically located TVT, without genital occurrence, that was successfully treated by surgery and chemotherapy. This report also indicates that TVT is also an important differential diagnosis of spinal neoplasia.