Canine Transmissible Venereal Tumor, often called CTVT or TVT, is a unique type of cancer affecting dogs and other canids. Unlike most cancers, which arise from the host’s own cells, CTVT is a naturally occurring, transmissible cancer cell line. This means the tumor itself is the infectious agent, spreading as living cancer cells directly from one dog to another.
Understanding Canine Transmissible Venereal Tumor
Canine Transmissible Venereal Tumor is biologically distinct because it is not caused by a virus or bacteria, but by the direct transfer of living cancer cells. These cells originate from a single founder dog that lived 6,000 to 11,000 years ago. The tumor cells are essentially a parasitic allograft, meaning they are genetically distinct from the host dog and perpetuate themselves by moving between individuals. This ancient cancer lineage has since spread globally, with its distribution often linked to populations of free-roaming dogs.
How CTVT Spreads
CTVT spreads through direct physical contact, with sexual contact being the most common mode of transmission. During mating, tumor cells can transfer from an infected dog to another. Beyond sexual activity, the tumor can also be transmitted through other close social behaviors, including licking, sniffing, or minor bites. Transmission from a mother dog to her puppies through grooming has also been documented.
Recognizing the Signs
The clinical signs and appearance of CTVT can vary depending on the tumor’s location. Tumors most commonly appear on the external genitalia of both male and female dogs, such as the penis and prepuce in males or the vulva in females. These growths often have a characteristic cauliflower-like, nodular, or multilobulated appearance, ranging in size from small nodules of 5 mm to large masses exceeding 10 cm. The surface of the tumor is frequently ulcerated, inflamed, and may bleed easily.
While genital tumors are typical, CTVT can also manifest in extragenital sites, including the mouth, nose, eyes, and even the skin. Tumors in the nasal cavity might cause nosebleeds or other discharge, while oral tumors may present as cauliflower-like nodules on the tongue or other parts of the mouth. Affected dogs might exhibit excessive licking of the genital areas, discomfort during urination, or visible bleeding from the affected sites. These tumors often grow rapidly, though some may undergo spontaneous regression.
Diagnosis and Treatment Approaches
Veterinarians diagnose CTVT through a cytological examination, which involves analyzing cells from the tumor under a microscope. Fine-needle aspirates or impression smears reveal characteristic large, round cells with distinct central nucleoli and clear cytoplasmic vacuoles, making diagnosis straightforward. While less common, a biopsy and histological examination may be used in atypical cases or when differentiating CTVT from other round cell tumors. Imaging techniques like X-rays and ultrasounds can also be used to detect internal masses if spread to other organs is suspected.
Chemotherapy is the most effective treatment for CTVT, with vincristine sulfate being the medication of choice. This drug is administered intravenously once a week, and most cases achieve complete remission within three to eight doses. The success rate of vincristine sulfate is high, even for tumors that have spread to other areas. While surgery or radiation therapy can also be effective, chemotherapy is preferred due to the anatomical locations of many tumors, which can make complete surgical removal challenging and prone to recurrence.
Prognosis and Prevention
The prognosis for dogs with CTVT is excellent with appropriate treatment, particularly with vincristine sulfate chemotherapy. Most dogs achieve complete remission, meaning all visible tumor masses disappear. After successful treatment, dogs develop immunity to future CTVT challenges.
Preventing the spread of CTVT primarily involves responsible pet ownership practices. Spaying or neutering dogs can significantly reduce roaming and unsupervised breeding, thereby limiting opportunities for transmission. Avoiding contact with unknown or stray dogs, especially those showing suspicious growths or signs of illness, is another important preventive measure. Regular veterinary check-ups can help in early detection and prompt treatment, which further aids in controlling the disease in canine populations.