Venereal Tumors (Sexually Transmitted Tumors) in Dogs
- Occurrence: very rare
- Location of disease: Abdomen/pelvis
When to visit the vet?
Non-urgent see a veterinarian within 2–3 days
If the condition worsens / symptoms persist, consult a veterinarian.
The most important facts at a glance
Canine Transmissible Venereal Tumor (CTVT) is a unique, transmissible tumor in dogs that is primarily transmitted during mating, but also through sniffing or licking of tumor tissue from one dog to another. These tumors do not originate from the affected dog’s cells, but are transmitted as “foreign” tissue from an infected dog to another. Scientific studies have shown that CTVT cells are genetically descended from a dog that lived several thousand years ago. Symptoms include red masses on the penis or vagina, increased licking in the genital region, and blood droplets. Diagnosis is made through clinical examination and cytological analysis. Treatment options are primarily chemotherapy with vincristine, sometimes combined with surgical removal or radiation therapy. The prognosis is generally good, especially with early diagnosis and treatment. For prevention, sexual contact between dogs should be controlled, for example through castration / neutering or sterilization, and dogs should be kept away from potentially infected animals. Regular veterinary examinations and awareness about the disease also contribute to reducing its spread.
Causes
Venereal tumors (TVT) are one of the few types of cancer considered transmissible. These tumors are unique because they do not arise from the affected dog’s own cells, but rather through the direct transmission of tumor cells from an infected dog to another. This occurs primarily during mating, but can also happen through sniffing or licking of tumor tissue.
TVT belongs to a very small group of transmissible cancers that occur in animals, including the Tasmanian devil, which suffers from a similar facial tumor. In dogs, these tumors represent a form of allotransplantation, where the tumor cells themselves act as “foreign” tissue that can evade the new host’s immune system.
Scientific studies show that TVT cells are genetically descended from a single original dog that lived several thousand years ago. This makes TVT one of the oldest known continuous cell lines in the world. The ability of tumor cells to evade the immune system is enabled by genetic and molecular mechanisms that are still the subject of intensive research.
Symptoms
Symptoms of TVT (CTVT) are often limited to the external reproductive organs, but can also occur at other body sites if transmission occurs through contact with other mucous membranes. In male dogs, masses commonly appear on the prepuce, while in female dogs the vulva may be affected. These tumors appear as cauliflower-like masses that often bleed or ulcerate.
In addition to visible tumor masses, affected dogs may also show signs of discomfort, such as lethargy, loss of appetite, and in severe cases, weight loss. If the tumors metastasize to the oral cavity or nasal area, breathing problems or difficulty swallowing may occur.
Diagnosis
Diagnosis of CTVT is usually made through a combination of clinical examination and cytological analysis. The veterinarian will perform a biopsy or fine-needle aspiration of the suspicious mass to obtain cells for microscopic examination.
Cytological examination typically shows large, round tumor cells with a characteristic appearance. These cells have a high nuclear-to-cytoplasmic ratio, multiple nucleoli, and a moderate amount of bluish cytoplasm. A definitive diagnosis is supported by these microscopic features.
Therapy
Treatment of CTVT is usually very effective, with chemotherapy being the preferred method. Vincristine is the most common chemotherapeutic agent, administered weekly over several weeks. This treatment leads to complete remission in most cases.
In some cases, surgical removal of the tumors may also be considered, especially if the tumors are small and easily accessible. However, surgical removal alone carries a higher risk of recurrence, which is why it is often combined with chemotherapy.
Radiation therapy is another treatment option that can be used in cases where chemotherapy is contraindicated or tumors cannot be surgically removed. However, this method is less common and is primarily offered in specialized veterinary oncology centers.
Prognosis and follow-up care
The prognosis for dogs with CTVT is generally very good, especially when the disease is detected and treated early. The majority of dogs respond well to chemotherapy and achieve complete remission. The relapse rate is low when therapy is performed correctly.
In cases where tumors are not treated in time or when they metastasize, the prognosis may be worse. However, metastases are relatively rare in CTVT and usually occur in the regional lymph nodes or skin.
Prevention
The most effective method for preventing CTVT is controlling the reproductive behavior of dogs. This can be achieved through castration / neutering or sterilization to minimize sexual contact, which is the main route of transmission for tumor cells.
Furthermore, dog owners should ensure their pets are kept away from unknown or stray dogs that may be infected. Regular veterinary examinations and awareness of CTVT symptoms can also help prevent the spread of the disease.
Another important aspect of prevention is educating dog owners about the risks and transmission routes of CTVT. An informed community can help reduce the spread of these tumors in the dog population.
Outlook on current research
Venereal tumors in dogs (TVT) are special types of cancer that are “transmitted” from dog to dog during mating. Researchers have shown that this is a very old tumor line that has survived for centuries. Today, treatment is usually with the drug vincristine—often very successfully. Research now asks: Why do some tumors heal less well? And how can relapses be prevented?
One focus is the immune system. Many TVT cells “hide” from immune cells. Teams are therefore testing strategies that reactivate the body’s own defenses or combine them effectively with chemotherapy. At the same time, researchers are looking for simple progression markers, such as tiny tumor traces in the blood (circulating DNA), to detect early whether treatment is working and when it can be safely discontinued.
Imaging and tissue analyses should better predict when tumors spread beyond the genital area. Worldwide studies on prevalence also help plan prevention (e.g., castration / neutering and stray dog programs). Goals are shorter, gentler therapies with lasting success.