Primary corneal pigmented squamous cell carcinoma with concurrent canine papillomavirus type 17 infection in a dog.

Case history: A 9-year-old, spayed, female Golden Retriever presented with an 18-month history of small spots of opacification on the left cornea, a 3-4-month history of a raised spot on the left cornea, and a watery left eye. As a puppy, the dog had sustained an injury to the left cornea. Self-limiting, presumed papillomaviral warts were diagnosed on the face when the dog was 8 months old.

Clinical findings and initial treatment: A full ophthalmic examination revealed a well-circumscribed, pigmented, raised mass immediately adjacent to three smaller pink masses on the left cornea. The corneal tumour was resected by superficial keratectomy. The cornea was treated with topical peginterferon alfa-2a drops post-operatively.

Pathological and molecular findings: The mass was histologically diagnosed as an incompletely excised corneal pigmented squamous cell carcinoma (pSCC) displaying both exophytic growth and superficial stromal invasive characteristics and fine granular brown melanin pigment within the cytoplasm of neoplastic cells. Superficial cells showed evidence of papillomavirus-induced cell changes including enlarged cells with blue-grey cytoplasm and darkly basophilic keratohyalin granules. Canine papillomavirus type 17 (CPV17) DNA sequences were amplified from the carcinoma by PCR using consensus papillomavirus primers.

Diagnosis: Primary corneal pigmented squamous cell carcinoma with concurrent canine papillomavirus type 17 infection.

Outcome: Tumour recurrence was observed 2 years 9 months after surgery. Topical peginterferon alfa-2a drops were recommenced and superficial keratectomy surgery was repeated with concurrent adjunctive strontium 90 plesiotherapy. At the time of writing, the left cornea has healed well with mild fibrosis and vascularisation continuing to reduce.

Clinical relevance: This is the first report of a pSCC of the cornea in any veterinary species. Prominent papillomaviral cytopathology was visible in the corneal pSCC, and PCR confirmed the presence of CPV17.This report expands the differential diagnoses for pigmented corneal masses in dogs. It highlights the importance of obtaining a histopathological diagnosis for pigmented corneal lesions, as the clinical disease course, prognosis and treatment options vary between lesions of different aetiologies. Corneal SCC is locally invasive and can recur without complete excision. Early surgical intervention with clean margins can be curative and restore corneal clarity, vision and patient comfort.