What are transmissible venereal tumors (TVTs)?
Transmissible venereal tumors (TVT) are tumors that arise from the dysregulated growth of cells called histiocytes. Histocytes are a type of immune system cell found in many areas of the body, including the skin. TVTs develop from skin histiocytes.
TVTs are malignant (cancerous) tumors. Different from other cancers, TVTs can spread between dogs. It is sexually transmitted through direct skin-to-skin contact with the tumor that results in cancer cells being transplanted from dog to dog. This type of tumor is more commonly seen in tropical and subtropical areas, particularly in Central/South American, the southern United States, Asia, and Africa, though it does occur world-wide. Dogs of any breed, age, or sex are susceptible, but it is most commonly observed in mixed-breed dogs, dogs that are sexually ‘intact’ (not spayed or neutered), and stray and free-roaming dogs.
What causes this cancer?
It is suspected that this type of cancer developed thousands of years ago in wolves and wild dogs through a mutation in the basic genetic material of the histiocytes. Additional genetic mutations in these cells are believed necessary for them to become malignant (cancerous).
The most common cause of this cancer is direct contact with a dog with TVT, which includes sexual contact (intercourse), licking, biting, and sniffing the tumor affected areas.
What are the signs that my dog has this type of tumor?
The signs of this type of tumor in your dog are entirely dependent on the location of the tumor. If located on the penis/prepuce or vulva, there may be irregular thickening of the tissue, discomfort, intermittent bleeding, or bruising.
You may notice your dog excessively licking the area. If located within the mouth or on the tongue, you may observe ‘cauliflower-like’ nodules that grow and continue to grow in these areas. They may ulcerate and bleed.
How is this type of tumor diagnosed?
This type of tumor is usually diagnosed via cytology. Cytology is the microscopic examination of cell samples. Cell samples can be collected either by swabbing the area with a cotton-tipped swab or by fine needle aspiration (FNA). FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor.
After collection, the cells are placed onto a microscope slide. A veterinary pathologist then examines the slide under a microscope. In some cases, the results of the cytology may not be entirely clear, and a biopsy may be necessary. A biopsy is the surgical excision of a piece of tumor. The piece (or pieces) of the tumor are then examined by a veterinary pathologist under the microscope. This is called histopathology.
How does this cancer typically progress?
In the majority of cases, this cancer typically remains local, meaning that it affects only the area that originally came in contact with the cancer. Although this cancer may disappear on its own (spontaneous regression) due to an immune system response, this is extremely rare. TVTs usually continue to grow and can become increasingly bothersome without treatment. In rare cases, TVTs can metastasize (spread to other areas of the body), usually to the nearby lymph nodes.
"TVTs usually continue to grow and can become increasingly bothersome without treatment."
What are the treatments for this type of tumor?
Complete surgical excision, radiation therapy, and chemotherapy are effective treatments; however, chemotherapy is currently the treatment of choice. Complete surgical excision may be difficult (and often cannot be achieved) due to the location of these tumors. Surgery alone often leads to recurrence. If there is resistance to chemotherapy, radiation therapy may be required. The prognosis for total remission with chemotherapy or radiation therapy is good.
Is there anything else I should know?
If your dog has been diagnosed with TVT, it is most likely that it was contracted from another dog. Until your dog is treated and your veterinarian determines that treatment successfully eliminated the tumor, contact with other dogs should be avoided. These tumors can become bothersome, ulcerate, and bleed. If your pet has developed a TVT, treatment should be pursued as soon as possible, both to avoid the transfer of the disease to other dogs and the risk (although rare) of metastasis.