Progression of aural plaques to squamous cell carcinoma in a horse.

ABSTRACT

BACKGROUND: Aural plaques are associated with and thought to be caused by one or more Equus caballus papillomaviruses (EcPV). Aural plaques have not previously been reported to be associated with squamous cell carcinoma (SCC). HYPOTHESIS/OBJECTIVES: To describe a horse with aural plaques and squamous cell carcinoma (SCC) on the right pinna. ANIMALS A 28-year-old thoroughbred gelding presented for multiple plaques and a mass on the right pinna. METHODS AND MATERIALS Pinnal resection, histopathological investigation, multiple conventional PCRs for papillomavirus DNA and Sanger sequencing were performed. RESULTS: Multiple, raised, pale tan, fronded plaques covered 60% of the concave surface of the right pinna. Focally these plaques coalesced into an exophytic ulcerated mass near the base of the pinna. Multiple aural plaques and a SCC were diagnosed histopathologically. EcPV4 was detected via PCR in a sample of the SCC. CONCLUSIONS AND CLINICAL IMPORTANCE This report demonstrates the possibility of malignant transformation from aural plaques to SCC on the pinna of a horse. To the best of the authors' knowledge, this is the first report of EcPV4 associated with SCC.