A five-year-old Arabian mare was examined after a six-month history of a painless swelling on the conjunctiva of her right eye. Clinical assessment revealed a dense, fleshy, and uniformly smooth lesion, initially suspected to be a conjunctival tumor. Microscopic study demonstrated an inward-growing mass made up of elongated papillary folds of thickened squamous epithelium supported by slender fibrovascular cores. Within the lesion, cellular irregularities and infiltration of neighboring tissue—hallmarks of squamous cell carcinoma—were evident. The findings supported a diagnosis of an inverted papilloma that had undergone malignant change. During a 12-month follow-up period, no regrowth was observed. According to available data, this appears to be the first documented occurrence of inverted papilloma in a horse; its evolution toward carcinoma underscores the need to recognize this lesion among potential conjunctival tumors when determining diagnosis and treatment.
