Transmissible Tumor Disease of the Genital Organs in Dogs (Venereal Tumors)
- 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 from one dog to another during mating, but also through sniffing or licking of tumor tissue. These tumors do not originate from the affected dog’s own 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 area, and drops of blood. Diagnosis is made by clinical examination and cytological analysis. Treatment options primarily include 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 of the disease also contribute to containing its spread.
Causes
Venereal tumors (TVT) are among 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 one 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
The symptoms of TVT (CTVT) are often limited to the external reproductive organs, but can also occur in other body areas if transmission occurs through contact with other mucous membranes. In male dogs, masses often 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 tumors metastasize to the oral cavity or nasal area, breathing problems or difficulty swallowing may occur.
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 they 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 metastasize, the prognosis can be worse. However, metastases are relatively rare in CTVT and mostly occur in the regional lymph nodes or in the 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 specific types of cancer transmitted from dog to dog during mating. Researchers have shown that it is a very old tumor lineage that has persisted for centuries. Today, treatment usually involves the drug vincristine – often very successfully. Research is now asking: Why do some tumors respond less well to treatment? 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 sharpen the body’s own defenses again or combine them effectively with chemotherapy. In parallel, they are looking for simple progression markers, such as tiny tumor traces in the blood (circulating DNA), to detect early whether the treatment is working and when it can be safely concluded.
Imaging and tissue analyses should better predict when tumors spread beyond the genital area. Worldwide prevalence studies also help plan prevention (e.g., castration / neutering and stray dog programs). Goals are shorter, gentler therapies with lasting success.
Frequently Asked Questions (FAQs)
1. What are venereal tumors in dogs?
2. How do I recognize such a tumor?
3. Does this hurt my dog?
4. Can the tumor also occur outside the genitals?
5. How does the veterinarian make the diagnosis?
6. How is it treated?
7. Are there side effects of therapy?
8. Is surgery necessary?
9. Is the tumor contagious to humans or other pets?
10. How can I prevent it?
Literature
- Pimentel, P. A. B., Giuliano, A., Odatzoglou, P., Ignatenko, N., Wenceslau, R. R., Almeida, I. O., da Silva, P. H. S., Costa, M. P., & Horta, R. S. (2025). Clinical guidelines for canine transmissible venereal tumour treatment: Systematic review and meta-analysis. Veterinary and Comparative Oncology, 23(2), 125–140. https://doi.org/10.1111/vco.13038
- Ganguly, B., Das, U., & Das, A. K. (2016). Canine transmissible venereal tumour: A review. Veterinary and Comparative Oncology, 14(1), 1–12. https://doi.org/10.1111/vco.12060
- Faro, T. A. S., & de Oliveira, E. H. C. (2023). Canine transmissible venereal tumor—From general to molecular characteristics: A review. Animal Genetics, 54(1), 82–89. https://doi.org/10.1111/age.13260
- Murchison, E. P., Wedge, D. C., Alexandrov, L. B., Fu, B., Martincorena, I., Ning, Z., Tubio, J. M. C., Werner, E. I., Allen, J., De Nardi, A. B., Donelan, E. M., Marino, G., Fassati, A., Campbell, P. J., Yang, F., Burt, A., Weiss, R. A., & Stratton, M. R. (2014). Transmissible dog cancer genome reveals the origin and history of an ancient cell lineage. Science, 343(6169), 437–440. https://doi.org/10.1126/science.1247167
- Baez-Ortega, A., Gori, K., Strakova, A., Allen, J. L., Allum, K. M., Bansse-Issa, L., Bhutia, T. N., Bisson, J. L., Briceño, C., Castillo Domracheva, A., Corrigan, A. M., Cran, H. R., Crawford, J. T., Davis, E., de Castro, K. F., de Vos, A. P., Delgadillo Keenan, L., Donelan, E. M., Espinoza Huerta, A. R., et al. (2019). Somatic evolution and global expansion of an ancient transmissible cancer lineage. Science, 365(6452), Article eaau9923. https://doi.org/10.1126/science.aau9923
- Setthawongsin, C., Teewasutrakul, P., Tangkawattana, S., Techangamsuwan, S., & Rungsipipat, A. (2019). Conventional-vincristine sulfate vs. modified protocol of vincristine sulfate and L-asparaginase in canine transmissible venereal tumor. Frontiers in Veterinary Science, 6, Article 300. https://doi.org/10.3389/fvets.2019.00300
- Pimentel, P. A. B., Oliveira, C. S. F., & Horta, R. S. (2021). Epidemiological study of canine transmissible venereal tumor (CTVT) in Brazil, 2000–2020. Preventive Veterinary Medicine, 197, Article 105526. https://doi.org/10.1016/j.prevetmed.2021.105526
- Castro, K. F., Strakova, A., Tinucci-Costa, M., & Murchison, E. P. (2017). Evaluation of a genetic assay for canine transmissible venereal tumour diagnosis in Brazil. Veterinary and Comparative Oncology, 15(2), 615–618. https://doi.org/10.1111/vco.12205