Topical treatment of equine sarcoids with imiquimod 5% cream or Sanguinaria canadensis and zinc chloride – an open prospective study

Abstract

Background: Equine sarcoids are the most prevalent skin neoplasm in horses worldwide. Although several treatments are available, none are consistently effective and recurrence is common. Objectives: To evaluate the efficacy and safety of topical imiquimod 5% cream and Sanguinaria canadensis + zinc chloride for treatment of equine sarcoids and investigate possible systemic effects on distant untreated sarcoids. Animals/Tumours: Twenty-five client-owned horses with a total of 164 tumours were included in the study. Fifty-seven tumours were treated and 107 tumours were left untreated. Methods and materials: Skin biopsy samples were collected from a minimum of one tumour per horse and the rest were diagnosed based on clinical appearance as likely sarcoids. Imiquimod 5% (A) was applied three times weekly, while Sanguinaria canadensis + zinc chloride (X) was applied every fourth day after a six day daily initiation phase. Treatment continued until clinical remission or for a maximum of 45 weeks, with a long follow-up period (mean 34 months). Skin biopsy samples of sarcoid lesions were re-taken before treatment termination and at follow-up if the owner gave consent. Results: Complete remission was recorded in 84.4% (A) and 75.0% (X) of the tumours. Relapse was recorded in 7.3% (A) and 21.4% (X). Spontaneous remission was observed in 1.9% of untreated tumours. No systemic effect on untreated tumours was detected. During treatment varying degrees of local inflammatory reaction were common. Conclusions and clinical relevance: Both treatments were considered effective and safe. Smaller tumours responded more favourably to treatment. Relapse rate was low and not observed in sarcoids with repeat biopsies before treatment termination.