Papillomas are benign tumors that originate from the squamous epithelial cells. Several types of papilloma have been described. In puppies, papillomas may appear as tufts of cauliflower-like tissue growing on the lips and in the mouth. These papillomas are viral in nature and usually disappear in 2 to 3 months as the puppy's immune system matures. Occasionally, in severe cases difficulty swallowing and breathing may develop which will require surgical removal and electrocautery, a procedure involving burning a tissue with electrical current using a specially designed apparatus. Warts, or singular papillomas, are found on the skin of older dogs. If they are small and look like mushrooms on a stalk or just finger-like, they are typically nothing to worry about. However, if they grow in size and ulcerate, they should be removed and biopsied. If they are black and growing on the eyelids or lips, they should be removed and biopsied to rule out the possibility of malignant melanoma.
Canine oral papillomavirus (COPV) causes canine oral papillomatosis, the most common form of papilloma virus disease, which typically regresses without treatment. Viral papillomas are common tumors occurring in puppies and young dogs. These multiple tumors are contagious. Areas primarily affected are mouth (from lips to esophagus), nostrils, and on the eyelid and adjacent haired skin. The lesions begin as small, flat, grayish papules, and can grow rapidly into larger cauliflower-like masses. When the mouth is severely affected, chewing and swallowing is difficult. Canine viral papillomatosis can rarely transform to squamous cell carcinoma.
Canine Papillomavirus Variants
There are three forms of papillomatosis: (1) canine exophytic cutaneous papillomatosis; (2) pigmented epidermal plaques; and (3) exophytic papillomas. Pigmented epidermal plaque (PEP) has been reported in the Pug, Miniature Schnauzer, Chinese Shar-pei, English Setter (rare), and one English Pointer. Affected dogs have multiple cutaneous discolored spots in the skin. The dark pigmentation in the lesions results from an abnormal distribution of the dark pigment melanin within the epidermis (outermost skin layer).
Exophytic papillomas are papillomas growing outward which are similar to common warts in humans. Most exophytic papillomas on haired skin are caused by a papilloma virus that is different from canine oral papillomavirus. Multiple or numerous lesions may have a broad base or positioned on a stalk. This form of the disease is referred to as cutaneous papillomatosis. Lesions are typically less than 1 cm in diameter. Overgrowth of skin cells may be severe enough to form a cutaneous horn. Exophytic viral papillomas occur mainly on the face, ears and limbs, but usually do not involve the pads. The papillomas can occur at any age, but most often seen in dogs less than 2 years of age. Most exophytic papillomas regress without treatment within weeks or months. Transformation of exophytic papillomas into malignant tumors is extremely rare.
Cutaneous inverted papilloma usually appear as multiple, raised, firm masses that are less than 2 cm in diameter and growing inward. Most of them occur on the abdomen, and, unlike exophytic papillomas, they do not regress spontaneously. The disease is quite rare in dogs and occur primarily in dogs less than 3 years of age. The Whippet, Irish Setter, Beagle, Bernese Mountain Dog, Cocker Spaniel, Great Dane, and Kerry Blue Terrier are reported to be predisposed to viral papillomatosis.
Squamous cell carcinoma (SCC) originates from squamous epithelial cells and results from malignant transformation of multiple plaques which emphasizes the need to recognize pigmented epidermal plaque and to control its progression. Antiviral and antineoplastic therapy, such as low-dose oral IFN-alpha, may be an effective component of the therapeutic management of both PEP and papillomavirus-associated cutaneous neoplasia. SCC is common in dogs and cats and usually affects older animals. Squamous cell carcinoma is typically seen around in large breed dogs, but any dog at any age can develop this type of cancer. Treatment options for dogs with squamous cell carcinoma include surgery, radiation, chemotherapy, and any combination thereof.
- Scott, Miller & Griffin. Small Animal Dermatology, 5th ed., 1995.
- Richardson RC et all. Common Skin Tumors of the Dog: A Clinical Approach to Diagnosis and Treatment. Compend. Cont. Educ. Pract. Vet. 6: 1080-1086, 1984.
- Nesbitt & Ackerman. Canine Cutaneous Neoplastic and Nonneoplastic Tumors and Cysts. In: Canine & Feline Dermatology: Diagnosis and Treatment. Veterinary Learning Systems, Trenton, New Jersey, 1998.
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