Transmissible Venereal Tumor

What are transmissible venereal tumors?

Transmissible venereal tumors (TVTs) are tumors that arise from the dysregulated growth of skin cells called histiocytes. Histiocytes are a type of immune system cell found in many areas of the body, including the skin. TVTs are classified as a type of round cell tumor and are malignant (cancerous).

Unlike other cancers, TVTs can spread between dogs. They are sexually transmitted through direct skin-to-skin contact with the tumor, causing cancer cells to be transferred from dog to dog. 

This type of tumor occurs worldwide, but is more commonly seen in tropical and subtropical areas, particularly in Central and South America, the southern United States, Asia, and Africa. TVTs are most commonly observed in mixed-breed dogs, sexually intact dogs (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 due to a mutation in the genetic material of histiocytes. It is believed that additional genetic mutations in these cells occur for the tumors to become malignant (cancerous).

The most common cause of this cancer in dogs is direct contact with a dog with TVTs, including sexual 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 tumor depend on its location. If the tumor is located on the penis or vulva, signs may include irregular thickening of the tissue, discomfort, intermittent bleeding, or bruising. You may notice your dog excessively licking the area. 

If the tumor is located in the mouth or on the tongue, you may observe “cauliflower-like” nodules growing 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. Your veterinarian will collect cell samples either by swabbing the area with a cotton-tipped swab or by fine needle aspiration (FNA). FNA involves using a small needle and syringe to collect a sample of cells directly from the tumor.

After collection, the cells are placed onto a microscope slide, and a veterinary pathologist examines the slide under a microscope. In some cases, the results of cytology may not be clear, and a biopsy may be necessary. A biopsy is the surgical removal of a small piece of the tumor. The piece of the tumor is then examined by a veterinary pathologist under the microscope—a process called histopathology.

How does this cancer typically progress?

In most cases, this cancer remains localized, meaning it affects only the area where it first developed. 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. This cancer may disappear on its own (spontaneous regression) due to an immune system response, but this is extremely rare.

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 the tumor is resistant to chemotherapy, radiation therapy may be required. The prognosis for complete remission with chemotherapy or radiation therapy is good.

Is there anything else I should know?

If your dog has been diagnosed with TVT, it most likely contracted it from another dog. Your dog should be treated as soon as possible to avoid metastasis and should not have contact with other dogs until your veterinarian determines that treatment successfully eliminated the tumor. These tumors can become bothersome, ulcerate, and bleed.