Comparison of intratumoral administration of cisplatin versus bleomycin for treatment of periocular squamous cell carcinomas in horses

Objective - To compare therapeutic benefits of intratumoral administration of cisplatin and bleomycin for squamous cell carcinoma of the eyelids in horses. Animals - 25 horses with 27 T2-stage periocular squamous cell carcinomas. Procedure - Horses were treated 4 times at 2-week intervals with a slow-release formulation of cisplatin (1 mg/cm³ of tissue) or bleomycin (1 IU/cm³ of tissue). A two-stage design was used to minimize me sample size in each treatment arm. Results - The local control rate at 1 year for lesions treated with cisplatin was 93 ± 6% and with bleomycin was 78 ± 10%. Difference in total control duration between the 2 treatment groups was not significantly different. A high tumor proliferative fraction index value was associated with a higher local (infield) control rate, but also with a higher riSK of marginal and regional recurrences. Tumors with a low proliferative fraction index value (< 28%) had 9.5-times higher (P = 0.0411) risk of recurrence than those with a high index value. Local acute reactions were similar in the 2 treatment groups, and chronic reactions were not observed. Conclusions - Cisplatin and bleomycin were effective anticancer agents for carcinoma of the eyelid in horses. Based on therapeutic benefit and treatment cost, cisplatin was found to be a better choice for intratumoral chemotherapy of eyelid carcinomas. Clinical Relevance - Results of this study confirm the value of intratumoral chemotherapy, using cisplatin, for treatment of cutaneous squamous cell carcinomas in horses.