Veterinary Hospital of the University of Pennsylvania
Definition: A benign exophytic neoplastic proliferation of the squamous epithelium caused by infection with papillomavirus
Synonyms: warts or verruca vulgaris
Epidemiology and Etiology
caused by a papovavirus, which is a double stranded DNA virus. Two different papovaviruses are thought to be present in the dog:
Canine Oral Papilloma Virus (COPV)- responsible for the oral papilloma
Canine Papilloma Virus (CPV)- responsible for the cutaneous and inverted papilloma
occur most commonly in dogs less than 3 years of age
does not show any sex predilection
(Normal Population %)
Breeds at Increased Risk
American Pit Bull Terrier
Jack Russel Terrier
Breeds at Decreased Risk
95% Confidence Interval
Papilloma Age Distribution
Clinical Presentation/Physical Exam Findings
They are usually solitary lesions.
There are three different presentations of canine papilloma virus.
Cutaneous Papilloma - solitary or multiple lesions found on the skin surface.
Inverted Papilloma - a benign endophytic (growing inward) proliferation of the epidermis.
Oral Papillomatosis- with multiple papillomas found in the oral cavity
Upon physical examination, the majority of cutaneous papillomas appear as a narrow base mass projecting upward and outward from a thickened epidermis.
On cut section these lesions often consist of multiple fronds with keratinous material accumulating on the surface and between the fronds.
The skin that surrounds the papillomas is usually normal but secondary bacterial infections may be found
Inverted papillomas are usually larger than cutaneous papillomas, solitary and endophytic.
They are located within the dermis and can extend into the subcutaneous as the tumor grows.
Keratinous material may accumulate in the center of the mass obscuring the finger-like projections that may be seen on clinical presentation.
These masses are usually well demarcated from the surrounding epidermis and dermis.
Three different histopathologic findings may be found with canine cutaneous papillomas. It is unclear at present whether this represents differences in virus subtypes of canine papillomavirus.
Papilloma- Papilliferous Subtype
This is the most commonly encountered papilloma and is characterized by:
the elongated rete at the periphery of the papilloma are slanted towards the center
papillae are supported by a thin core of dermal fibrous connective tissue
thickened stratum corneum, may be orthokeratotic or parakeratotic
granular cell layer is either absent or has very prominent enlarged keratohyaline granules in the cytoplasm
in some cells the normal cell eosinophilic (red) cytoplasm of the cells of the spinous layer is replaced by a grey-blue finely granular material (viral cytopathic effect)
occasional intranuclear pale basophilic inclusions (virus)
lymphoplasmacytic and neutrophilic infiltration of the dermis.
Papilloma- Infundibular Subtype
This subtype affects the infundibulum of the hair follicle and not the overlying epidermis. The histopathology is characterized by:
the overlying epidemis is hyperplastic
the follicular infundibulum is filled with parakeratin
there is an abrupt transition from normal epidermal keratinocyes to affected/infected cells
hyperplasia of basal and lower spinous layer
cells in the hyperplastic upper spinous layer have an abundant grey-blue cytoplasm
Fairly numerous intranuclear viral inclusion bodies, more readily seen on immunohistochemistry
Le Net subtype
Papilloma- Le Net Subtype
This subtype was originally described as pigmented popular lesions but other non-pigmented, non-papular lesions have been seen. The lesions may be exophytic or endophytic.
The histopathology of this subtype is characterized by:
intracytoplasmic, brightly eosinophilic fibrillar material (keratin) that occupied most of the cell
peripheral nucleus with basophilic intranuclear inclusion bodies
Inverted papillomas appear similar histologically to the papillerous subtype of cutaneous papillomas.
intranuclear eosinophilic inclusion bodies may be seen in some cells from the granular cell layer.
lymphocytes, plasma cells, and neutrophils may be seen, which is indicative of secondary inflammatory changes.
Many papillomas will regress spontaneously; however, regression may take anywhere from weeks to months to occur.
Spontaneous regression is due to cell mediated immunity and humoral immunity.
Failure to regress may be an indication of an underlying immunodeficiency or an immunocompromised animal (receiving corticosteroid therapy).
Some papilloma virus infections have been known to progress into carcinomas, primarily squamous cell carcinomas.
Goldschmidt, M.H., & Hendrick, M.J. (2002). Tumors of the skin and soft tissue. In D.J. Meuten (Ed.), Tumors in domestic animals 4 th ed (pp. 45-119). Iowa: Iowa State Press
Goldschmidt, M.H., & Shofer, F.S. (1998). Skin tumors of the dog and cat. Woburn, MA: Butterworth-Heinemann
Gross, T.L., Ihrke, P.J., & Walder, E.J. (1992). Veterinary dermatopathology: A macroscopic and microscopic evaluation of canine and feline skin disease. (pp. 327-485). St. Louis, Missouri: Mosby Year Book
Scott, D.W., Miller Jr., W.H., & Griffin, C.E. (1995). Muller and Kirk’s small animal dermatology 5 th ed. (pp. 990-1126). Philadelphia, PA: W.B. Saunders Company
World Health Organization (1998). Histological classification of epithelial and melanocytic tumors of the skin of domestic animals (2 nd series, vol 3). Washington, DC: Armed Forces Institute of Pathology
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