Transmissible venereal tumor (TvT) is a transplantable malignant neoplasm that most commonly affects the external genitalia of dogs. Cytogenetic characterization of the tumor reveals a consistent canine cellular complement throughout the world of 59 5 chromosomes, whereas the normal canine cellular complement is 78 chromosomes. The tumor is antigenic and the patient's immune response to the tumor defines the clinical course of disease. Spontaneous regression is common in dogs with experimentally induced TVT lesions, but the course in naturally occurring cases has been poorly documented. Clinical signs depend on tumor location, but a hemorrhagic discharge is often observed because of the friable nature of the mass. Metastasis occurs infrequently, with the most common sites being regional lymph nodes, distant lymph nodes, skin, and subcutaneous tissues. Most cases of this poorly differentiated round-cell tumor can be easily diagnosed with cytology. Treatment with radiation or vincristine is curative in more than 90% of cases. Clinical cases that are resistant to vincristine may still be effectively treated with radiation or doxorubicin.
