Equine Ocular Squamous Cell Carcinoma

Ocular squamous cell carcinoma (SCC) occurs commonly in the horse. Ultraviolet light exposure and lack of periocular pigment are thought to be the primary predisposing factors. Most tumors grow slowly and tend to be locally invasive; however, there is a 10% to 15% metastatic rate. The appearance of SCC varies greatly with its location. Corneal or limbal SCC is commonly raised, papillary, and light pink. The third eyelid may develop a scalloped appearance or become thickened. Eyelid SCC usually has a smooth mass effect and may be ulcerated. Treatment options include excision, cryotherapy, radiofrequency hyperthermia, radiotherapy, topical and intralesional chemotherapy with cisplatin or 5-fluorouracil, bacille Calmette-Guerin (BCG) cell wall extract, and carbon dioxide laser ablation. Generally, excision alone is not sufficient and ancillary therapy is recommended.