Laser‐induced photothermal ablation of equine dermal melanoma

Abstract

Equine dermal melanoma is a skin tumour most commonly seen in grey horses. Most grey horses will develop at least one tumour if they live long enough. Dermal melanoma and dermal melanomatosis are histologically identical, but dermal melanoma can present as either isolated single or multiple discreet lesions, while dermal melanomatosis presents as multiple coalescing lesions. These tumours are slow growing and have a predilection for the base of the tail, perineum, prepuce, parotid salivary gland and commissures of the lips. This report describes 980‐nm diode laser photothermal ablation as a non‐invasive treatment for equine dermal melanoma.To report the results of a series of horses that underwent laser photothermal ablation of equine dermal melanomas with a 980‐nm diode therapy laser.Retrospective case series.Horses were sedated for a standing procedure and restrained in stocks. A thermocouple needle was inserted deep to/into each lesion and the laser was applied either in contact or non‐contact fashion at 4–6 watts until a temperature of 50°C was reached. Masses that were significantly thicker than 1 cm had thermocouple needles placed at multiple levels. After 1 month, treatment sites were re‐evaluated. Lesions in which the planned treatment and follow‐up were completed were included.Fifty‐one individual melanomas in seven horses were included. Fifty lesions were classified as ‘Complete Response’ (CR). One thicker lesion had a ‘Partial Response’ (PR) but there was CR to the depth that temperature was reached.Only tumours approximating 1 cm in thickness are practical.Laser photothermal ablation using a 980‐nm therapy laser is a practical, non‐invasive and readily available modality for treating smaller equine dermal melanomas. Thickness rather than surface area is the main limitation for a single application.