A Review of Current Treatment Options in the Treatment of Ocular and/or Periocular Squamous Cell Carcinoma in Horses: Is There a Definitive “Best” Practice?

This review examines the most commonly reported treatment options for ocular squamous cell carcinoma (OSCC) and periocular squamous cell carcinoma (POSCC) in horses and proposes to conclude on the most viable method based on available published studies in terms of treatment outcome, known side effects, advantages, disadvantages, and reliability of available evidence. After a literature search for peer-reviewed published articles, seven most commonly reported on treatments for OSCC and/or POSCC were identified: surgery, photodynamic therapy, carbon dioxide (CO2) laser ablation, radiofrequency hyperthermia, cryotherapy, chemotherapy, and radiation therapy. Combination therapies were supported as a most successful recommendation; however, when considering site-specific outcomes, the following conclusions may be drawn: limbal squamous cell carcinoma (SCC) was most effectively treated with surgery and adjunctive therapy including CO2 laser ablation, mitomycin C, and brachytherapy; third eyelid SCC reported good outcomes when treated with surgery alone (clear margins) and in combination with brachytherapy for unclear margins; eyelid SCC, surgical resection was usually limited and most reports supported the use of adjunctive brachytherapy, although photodynamic therapy appeared to be a promising new treatment. It was deemed unreasonable to conclude on the best treatment for cornea, conjunctivae (palpebral and bulbar), and medial canthi in isolation because of lack of evidence. A consistently favored treatment for OSCC and/or POSCC in horses does not currently exist. The presentation of data in the literature and its lack of consistency make it impossible to statistically analyze and make comparative conclusions on treatment outcomes. This review provides a basis for further research to establish a best-practice protocol.