Oral Tumors: Papillomas and Fibropapillomas

What are papillomas and fibropapillomas?

Oral papillomas (warts) are benign, cauliflower-like tumors of the epithelial lining of the mouth and throat, although the esophagus may also be affected in severe cases. These tumors are caused by papillomaviruses, which are species-specific infections that can be transmitted to the skin or eyes if the protective outer epithelium is damaged. Oral papillomas are common in young dogs.

Once an animal is exposed to the virus, it takes approximately one to two months for papillomas to appear; this is called the incubation period. Once papillomas appear, they usually stay for about 2–3 months and then resolve on their own. After recovery, the animal will be immune to further infection. It is important to distinguish papillomas from malignant tumors that may also affect the mouth.

Fibropapillomas (sarcoids) are benign tumors that involve more of the connective tissue next to the epithelium. Young cats sometimes have several fibropapillomas in their mouths; these are similar to tumors on the face that are caused by a papillomavirus. Fibropapillomas disappear spontaneously but occasionally recur.

Rarely, puppies may have contact with a sheep-pox virus that causes “contagious pustular dermatitis” or "orf," and wart-like masses may appear in these pups. The tumors usually disappear spontaneously. Pox viruses are not species-specific, and this virus may infect people.

Papillomas and fibropapillomas (sarcoids) are rare in cats.

Why did my pet develop a papilloma or fibropapilloma?

The reason why a particular pet may develop this, or any tumor, is not straightforward. Most tumors seem to be caused by a complex mix of risk factors, some environmental and some genetic or hereditary. However, papillomas and fibropapillomas are probably all associated with virus infections.

Papillomaviruses cause most of these tumors, but other viruses may play a role in cats. Some papillomaviruses specific to people are associated with malignant tumors (the best known may be cervical cancer in women).

How will papillomas and fibropapillomas affect my pet?

These tumors are usually noticed as single or multiple polyp-like swellings on the gums or other parts of the mouth. Some growths ulcerate and bleed and they may become infected. Papillomas in the throat (pharynx) or esophagus are painful and may cause difficulty in swallowing.

How are papillomas and fibropapillomas diagnosed?

Clinically, these masses often have a fairly typical appearance. Radiographs (X-rays) may help differentiate them from malignant tumors, such as invasive squamous cell carcinomas, because the invasive cancers destroy adjacent bone.

For papillomas and fibropapillomas to be accurately diagnosed, the tissue must be examined under a microscope (histopathology). Your veterinarian will typically recommend a biopsy to obtain tissue samples for examination, as samples obtained with by fine needle aspiration will rarely provide a diagnosis. Your veterinarian will submit either a small part of the mass (biopsy) or the whole lump to a specialized diagnostic laboratory, where a veterinary pathologist will examine and diagnose the lesion.

The histopathology report also helps indicate how the tumor is likely to behave and rules out malignant cancers. The veterinary pathologist usually adds a prognosis that describes the probability of local recurrence or metastasis (spread to other parts of the body).

How are papillomas and fibropapillomas treated?

These viral tumors can disappear spontaneously in healthy animals due to the body's immune system activity. Occasionally, fibropapillomas may recur.

Surgical removal may be recommended for diagnostic purposes (to ensure that the mass is a benign "wart") or to treat a bleeding or infected growth. Removing these tumors too early may be counterproductive, though, because they start producing antigens about a month after infection, and these antigens activate the body’s protective immune response.

“These viral tumors can disappear spontaneously in healthy animals due to the body's immune system activity.”

If your veterinarian does not perform surgery, they may recommend medication to reduce inflammation, discomfort, or secondary infection, if present. Immune-stimulating medications such as interferon alpha, tigilanol tiglate, or imiquimod (Aldara®) may also be used. Other medications have been suggested as treatments, but evidence is lacking on their effectiveness.

How can I help my pet?

After surgery, your pet will need to wear an Elizabethan collar (E-collar or cone) to prevent trauma to the operation site. Your pet may require a special diet. Your veterinarian may request that you do not examine the surgery site in the early post-operative period. If your pet cannot eat or develops significant swelling or bleeding at the surgical site, contact your veterinarian immediately. If you require additional advice on post-surgical care, ask your veterinarian.

What is the prognosis for these tumors?

Most of these tumors are permanently cured by surgical removal or by the body's own immune system. Recurrence may indicate the tumor was incompletely removed, that it is deeper and more malignant (papillomatous squamous cell carcinoma), or that the pet's immune system is not fully competent.

Are there any risks to my family or other pets?

Papillomas and fibropapillomas are not transmitted from pets to people, but they can be transmitted between animals of the same species. Transmission requires close contact with an infected pet, damage to the surface of the mouth or lips, and a lack of immunity (either because the animal has not encountered the virus or because it lacks a fully effective immune system). The only exception is the rare sheep-pox virus that causes contagious pustular dermatitis; this virus can be transmitted to people.