CLINICAL-EVALUATION OF ETRETINATE FOR THE TREATMENT OF CANINE SOLAR-INDUCED SQUAMOUS-CELL CARCINOMA AND PRENEOPLASTIC LESIONS

Background: Tumors of the skin and subcutaneous tissue account for 30% of all canine neoplasms. Canine solar-induced squamous cell carcinoma (SCC) is the most frequently reported canine cutaneous neoplasm. Objective: The purpose of this study was to provide preliminary observations on the safety and efficacy of etretinate for the treatment of solar-induced SCC and associated preneoplastic lesions in dogs. Methods: Etretinate was administered to 10 dogs at 1 mg/kg twice daily for a minimum of 90 days. Results: Clinically, two dogs showed complete resolution of their preneoplastic lesions, three dogs had partial responses, two dogs maintained stable disease, and three dogs showed progression of lesions after 90 days of etretinate administration. Three dogs showed histologic improvement, four dogs showed no changes, and three dogs showed evidence of progressing SCC. Treatment-related biochemical abnormalities included reversible hypertriglyceridemia and transient serum liver enzyme elevations in three dogs. Conclusion: These preliminary findings suggest that etretinate, at the dosage administered, may provide therapeutic efficacy for solar-induced preneoplastic lesions in the dog, particularly for those multifocal lesions not easily managed by local methods of therapy.