Conjunctival Inverted Papilloma Progressing to Carcinoma. First Report in Horse.

A five-year-old, entire female Arabian horse with a 6-month history of a non-painful nodule on the conjunctiva of the right eye was evaluated. Ophthalmological examination showed a firm, smooth and fleshy conjunctival mass that raised the suspicion of a conjunctival neoplasm. Histological evaluations showed that the mass was composed of an endophytic growth consisting of numerous long papillary projections of hyperplastic stratified squamous epithelium supported by thin fibrovascular stalks. Typical features of squamous cell carcinoma with disorganized cell growth and infiltration of surrounding tissues were detectable within the mass. Inverted papilloma progressing to carcinoma was diagnosed. Follow-up examination showed that no local recurrence was present during the 12-month follow-up period. To the authors' knowledge, this is the first report describing the inverted papilloma in the horse and, due to its progression to squamous cell carcinoma, warns about the inclusion of the inverted papilloma in the differential diagnosis of conjunctival neoplasm and driven treatments.