Intralesional interferon alpha-2b as a novel treatment for periocular squamous cell carcinoma in horses

Objective To determine the safety and efficacy of perilesional human recombinant interferon alpha-2b (IFN alpha 2b) for treatment of periocular squamous cell carcinoma (PSCC) in horses. Animals studied Eleven horses (12 eyes) with PSCC were enrolled in this prospective clinical study with owner consent. Procedures Systemically healthy horses were included in the study following confirmation of PSCC via biopsy. Every two weeks for a maximum of six treatments, horses were sedated and perilesional injection of IFN alpha 2b (10 million IU) was performed. Tumors were measured prior to each injection and at one, three, and 12 months after treatment completion. A greater than 50% reduction in tumor size was considered positive response to treatment (i.e., partial or complete response). Development of anti-IFN alpha 2b antibodies was assessed using serum samples obtained after treatment initiation and compared with treatment responses. Antibody concentrations were analyzed using a mixed model. Statistical significance was considered p < 0.05. Results Each horse received four to six perilesional injections of IFN alpha 2b. Five of 12 eyes (4/11 horses) responded to treatment. Two of five eyes showed complete resolution of gross PSCC. No systemic adverse effects were seen. Local swelling occurred during treatment protocol in 6/11 horses but resolved without intervention. All horses developed serum anti-IFN alpha 2b antibodies. There was no evidence of statistical difference in antibody concentration between responders and non-responders. Conclusions Perilesional administration of IFN alpha 2b was found to be well-tolerated in horses with PSCC, and induced tumor regression in 42% of treated eyes. Treatment failure appears unrelated to the development of IFN alpha 2b antibodies.