Canine Transmissible Venereal Tumor (CTVT) is a unique contagious cancer affecting dogs. It spreads directly between dogs through the transfer of living cancer cells, not by a virus or bacteria. CTVT primarily affects sexually mature canines worldwide.
Understanding Canine Transmissible Venereal Tumor
CTVT is a histiocytic tumor, originating from immune system cells called histiocytes. Unlike most cancers, CTVT is transmissible; the tumor cells themselves are the infectious agents, spreading as an allograft. The tumor cells are not genetically related to the host dog.
This cancer is one of only three known transmissible cancers in mammals, alongside devil facial tumor disease in Tasmanian devils and contagious reticulum cell sarcoma in Syrian hamsters. Genetic analyses suggest CTVT originated from a single dog or wolf thousands of years ago and has since spread globally. The cells of CTVT tumors typically have an abnormal number of chromosomes, distinct from the normal canine count.
Transmission and Clinical Signs
CTVT primarily spreads through direct physical contact, most often during mating. Tumor cells can also transmit to non-genital areas through social behaviors such as licking, sniffing, or biting affected areas, leading to tumors on the face, mouth, or even in the eyes.
CTVT tumors commonly appear as masses on the external genitalia of both male and female dogs. In males, they are found on the penis and foreskin, while in females, they affect the vulva. These growths often have a characteristic cauliflower-like, nodular, or multilobulated appearance. They can be firm but also easily friable, meaning they may bleed or tear easily. Other signs include discomfort, excessive licking of the affected area, or intermittent bleeding and discharge from the genitals.
Diagnosis and Treatment Approaches
Veterinarians diagnose CTVT based on its physical appearance, the dog’s history, and a microscopic examination of cells. The most common diagnostic method is cytology, which involves examining cells obtained via fine needle aspiration (FNA) or an impression smear from the tumor. CTVT cells have a distinct appearance under the microscope.
While cytology is often sufficient for diagnosis, a biopsy may be performed for confirmation in atypical cases or when the results are unclear. Once diagnosed, chemotherapy is the most widely used and effective treatment for CTVT. Vincristine sulfate, administered intravenously, is the chemotherapy drug of choice.
Treatment with vincristine sulfate is typically given once a week. Most dogs achieve complete remission with 4 to 6 sessions of vincristine, though some cases may require up to 8 administrations. Other treatment options, such as surgery or radiation therapy, are less common. Surgery alone can be challenging due to tumor location and may lead to recurrence, while radiation therapy is reserved for cases that do not respond to chemotherapy.
Prognosis and Prevention Strategies
The prognosis for dogs with CTVT is generally excellent when appropriate treatment is administered. Most affected dogs make a full recovery, regardless of the tumor’s location or whether it has spread to other areas. It is important to complete the entire course of treatment as recommended by the veterinarian, as untreated tumors usually continue to grow and can become more problematic. While rare, spontaneous regression of CTVT can occur due to an immune system response, but most cases require intervention.
Spaying or neutering dogs is a highly effective prevention strategy, as it eliminates mating activity, which is the primary mode of transmission. Avoiding contact with stray or potentially infected dogs, particularly in areas where CTVT is more common, also reduces the risk. If a dog is diagnosed with CTVT, it is important to prevent contact with other dogs until a veterinarian confirms that the disease has been completely resolved.