Home » Pet Health » Canine Viruses and Infections » What is Canine Transmissible Venereal Tumor?


It might be surprising to know that some cancers can be contagious. One such cancer is the canine transmissible venereal tumor (CTVT). Researchers believe it originated thousands of years ago in wild dogs and wolves. These days, it is most common in dogs in close contact or in stray and wild dogs that are more sexually active. Because North America has greater control over stray dogs, breeding regulations, and effective treatments, the incidence of CTVT in companion animals is lower. But southern tropical and sub-tropical areas do experience higher rates.

What is CTVT?

CTVT is a cancer type found in male and female dogs, but studies indicate that it is more common in females since an infected male can mate with several females. However, the cancer is more likely to spread to other parts of the body in males than females, but the incidence of spread is still relatively low (0-17%).

The tumor develops because of the unregulated growth of immune cells called histiocytes. You can find the tumors primarily on the genitals, which allows for easy diagnosis of the disease, but lumps may also appear on the eyes, nose, mouth, anal area, and feet. Most often, CTVT spreads through mating, but it can also spread by licking, biting, and sniffing the tumor-affected area of an infected dog. Dogs of reproductive age, unneutered, and free-roaming are at the highest risk of contracting the disease, as well as dogs with a weakened immune system.

CTVT usually takes about 4 to 6 months to grow. Then it goes through a phase of stabilization, where there is little growth, followed by a spontaneous regression phase, where the tumor stops growing altogether, and the cancer cells disappear. However, not all tumors reach the final stage.

When the tumor grows, it usually begins as a single growing mass or nodule. The fusion of multiple nodules over time leads to a multi-nodular cauliflower-like appearance and discharge from the infected site. At the late stage, the tumors often ulcerate, become inflamed, and may bleed.

There are currently 3 classifications of canine venereal tumors, based on what the cells look like:

    1. Lymphocytic – when more than 60% of cells are round, have large central nuclei, and not many vacuoles (spaces) in the cytoplasm (clear, jelly-like substance in a cell), therefore looking like immune cells called lymphocytes
    1. Plasmacytic – when more than 60% of the cells have lots of cytoplasm, nuclei are situated to one side of the cell, and there are lots of vacuoles present
    1. Mixed type – a mixture of lymphocytic and plasmacytic cells

Although CTVT is common globally, there are steps you can take to prevent your dog from contracting this cancer. Several effective therapies, including chemotherapy, can successfully treat the tumor if your dog becomes infected, and you can take precautions to prevent the spread by isolating your infected dog until their illness resolves.

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Last Updated: July 29, 2022

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