Papilloma of the Skin

By Tammy Hunter, DVM; Debbie Stoewen DVM, MSW, RSW, PhD

Medical Conditions, Pet Services

What is a papilloma of the skin?

Papillomas are benign, sometimes multiple, tumors caused by viruses. They are commonly known as warts. The tumors often disappear spontaneously because the animal slowly develops immunity to them. Some papillomas may need to be removed surgically because they have become inflamed, infected, or they fail to regress over time.

Papillomas are uncommon in cats but common in dogs.


What causes papillomas?

After invading the cells of the dog or cat (the host), papilloma viruses insert their genetic information into the host cell's DNA and upset the normal processes of cell division, so that the cell divides abnormally and more frequently. The virus activates growth-promoting genes in the DNA (called oncogenes), and at the same time it inactivates suppressor genes that would normally limit cell proliferation and alters the genes that regulate normal, programmed cell death.

There are many different types of papilloma viruses and they occur in all species of animals, including people. Each species of animal has its own viruses and their related tumors. One of the best known is the warts of human feet (plantar wart).

How did my pet develop a papilloma tumor?

Your dog or cat has been infected with one of these papilloma viruses. All animals and people carry many viruses asymptomatically (without any clinical signs). However, pets with immature immune systems such as young dogs and puppies, and those that are immunocompromised (have a reduced ability to fight infections), are more prone to developing papilloma warts.

"Papilloma viruses can survive for long periods in the environment."

Papilloma viruses are very resistant to adverse conditions and can survive for long periods in the environment outside an animal. The virus is transmitted through direct contact from an infected pet or the pet’s environment (e.g., toys, food and water bowls, and bedding) and gain access to the body when the skin becomes softened by moisture, through cuts and abrasions, or with the assistance of ticks or biting insects (e.g., fleas, mosquitoes).

What are the clinical signs of papillomas?

Papillomas may appear as multiple oral (mouth) papillomas in young dogs, solitary cutaneous (skin) papillomas in dogs of any age, venereal (genital) papillomas, eyelid or conjunctival papillomas, and fibropapillomas. There are different viruses associated with different sites and in young and old animals. The lesions are usually inflamed polyps (warts), but they may be flat, scaly plaques, or inward growing hard masses. They may ulcerate (break open) and bleed. Papillomas that grow inwardly may cause pain, particularly if they are on the feet. In dogs, these tumors are most common on the feet or around and in the oral cavity.

In cats, papillomas are usually flat, plaque-like, and sometimes scaly. There may be one or more lesions, usually on the head, neck or limbs. There is also a fibropapilloma or sarcoid in cats caused by a subtype of papilloma virus. These are very rare and appear as one or more nodular masses usually on the head, neck, ventral abdomen, and limbs.

How are papillomas diagnosed?

Most papillomas have a typical appearance, although some of the more common sebaceous tumors in dogs are very similar. In order to obtain a definitive diagnosis, your veterinarian may perform a fine needle aspiration (FNA). FNA involves taking a small needle with a syringe and suctioning a sample of cells directly from the tumor and placing them on a microscope slide. A veterinary pathologist then examines the slide under a microscope.

In some cases, results from FNA may not be entirely clear and a biopsy may be necessary. A biopsy is the surgical excision of a piece of the tumor. In the case of papillomas, which tend to be small, the entire tumor may be removed. The tumor tissue is then examined by a veterinary pathologist under the microscope. This is called histopathology.

How do papillomas typically progress?

In healthy animals, papillomas do not spread to other areas of the body and are usually cured by surgery. Rarely, a tumor will regrow after surgery. If the viral infection persists because of an impaired immune system, additional papillomas may develop.

What are the treatments for this type of tumor?

Some papillomas will regress within 1-2 months because the animal develops immunity to it. However, some dogs have persistent tumors. The usual treatment is surgical removal.

In cats, papilloma viruses are associated with certain cancers (e.g., squamous cell carcinoma). Surgery is usually advised.

In humans, a topically applied immune-modifying agent that stimulates interferon production has successfully been used to treat papilloma virus lesions. It may have potential use in animals.


Is there any special care that I should provide to my pet?

It is important to prevent your pet from rubbing, scratching, licking, or biting the papilloma(s), all of which can cause inflammation, ulceration, infection, and bleeding. Any ulcerated (open) area needs to be kept clean.

"It is important to prevent your pet from rubbing, scratching, licking, or biting the papilloma(s), all of which can cause inflammation, ulceration, infection, and bleeding."

After surgery, you will need to keep the incision site clean and dry and prevent your pet from rubbing, licking, biting, or scratching at it. Report any loss of sutures or significant swelling or bleeding to your veterinarian. If you require additional advice on post-surgical care, please contact your veterinarian.

Since papillomas are caused by a virus, are there any risks to my family?

No, although this is an infectious tumor, the viruses are species specific and not transmissible to humans. The tumors in dogs, cats, and people are not related nor are they transmitted between species.

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