Signalment: 2-year-old male neutered mix K9.
History: Adopted from El Paso as a stray about 1.5 years ago and was neutered at that time. He has about a 1-year history of licking his penis that progressed to intermittent hemorrhagic discharge. Initially, the owners thought the small amount of blood they were finding was from him chewing his rawhides and sticks but then noted it was coming from his penis.
Due to the patient’s aggressive temperament, he was sedated for an exam, and a small piece of friable, fleshy tissue was noted when the prepuce was retracted. This was sent for histopathology.
A histopathology report from TVMDL dated 10/30/2025 described a round cell neoplasm, favoring a Transmissible Venereal Tumor (TVT) over lymphoma, though lymphoma could not be conclusively excluded without further testing.
The patient was started on vincristine and rechecked one week later. See post-treatment photos below. Once therapy is initiated, most patients show a rapid and noticeable response.
Case Discussion
Canine Transmissible Venereal Tumor (CTVT) is a naturally occurring transmissible neoplasm characterized by the direct transfer of viable tumor cells between dogs.
Transmission occurs predominantly during coitus, although nonsexual transmission through close mucosal contact has been documented. CTVT is most prevalent in regions with large free-roaming dog populations and limited access to population control measures.
CTVT primarily affects young, sexually intact dogs, with no consistent breed or sex predilection. Dogs in tropical and subtropical regions are disproportionately represented. Immunocompromised or malnourished animals may be predisposed to more aggressive disease, including rare metastatic spread. Despite its transmissible nature, CTVT is typically localized at presentation, reflecting a balance between tumor immune evasion and eventual host immune recognition.
Clinically, CTVT most often presents as a friable, multilobulated, hemorrhagic mass involving the genital mucosa, including the penis, prepuce, vulva, or vaginal vestibule. Ulceration and serosanguineous discharge are common, and lesions bleed readily with minimal manipulation. Extragenital involvement, including nasal, oral, cutaneous, or conjunctival sites, occurs less frequently and is often associated with nonsexual transmission. Clinical signs are typically localized, although regional lymphadenopathy may be observed.
Diagnosis is most commonly achieved via cytologic examination, which is often definitive. Cytologic features include a monomorphic population of round cells with moderate to abundant vacuolated cytoplasm, centrally located nuclei, and coarse chromatin. Mitotic activity varies with the tumor growth phase. Histopathology is reserved for atypical cases and demonstrates sheets of round cells with scant supporting stroma. Routine hematologic and biochemical parameters are generally unremarkable, and advanced staging is rarely required in the absence of clinical suspicion for metastasis.
Vincristine chemotherapy remains the treatment of choice for CTVT, with reported complete remission rates exceeding 90%. The standard protocol involves weekly intravenous administration at 0.5–0.7 mg/m², with most tumors resolving within three to eight treatments. Vincristine resistance is uncommon but may necessitate alternative chemotherapy agents, such as doxorubicin, or the use of radiation therapy in select cases. Surgical excision alone is not recommended due to high recurrence rates and the risk of tumor cell implantation.
The prognosis for dogs with CTVT is excellent when treated appropriately. Metastatic disease is rare, occurring in fewer than 5% of cases, and is most commonly observed in immunocompromised individuals. Even in advanced cases, therapeutic response is often favorable with appropriate intervention.
For questions regarding diagnosis, treatment protocols, or case-specific considerations, the team at West Texas Veterinary Specialists is always happy to collaborate and provide support.
Avenelle Turner DVM, DACVIM (Oncology)