Clinical outcomes of intratumoural para‐toluenesulfonamide treatment in equine melanoma

Summary

Equine melanoma is one of the most common cutaneous neoplasms in horses and is particularly prevalent in grey horses. Although these tumours often demonstrate indolent biological behaviour, some progressively develop locally invasive or malignant characteristics over time, making treatment decisions challenging in clinical practice. This case series describes the clinical outcomes of intratumoural para‐toluenesulfonamide (p‐TLS) treatment in seven horses with cutaneous melanoma managed under field conditions. Seven horses with histopathologically confirmed melanoma were treated with intratumoural p‐TLS at approximately weekly intervals, and tumour response was assessed through clinical examination, tumour measurements and serial photographic documentation. Clinical complete response was achieved in six of seven horses, while one horse showed partial response. Local tumour necrosis and sloughing developed in all cases and were followed by progressive wound healing. Mild treatment‐related adverse effects, including transient local inflammation and reduced appetite, were observed but were self‐limiting. Follow‐up duration ranged from 107 to 765 days, with one case of local recurrence. Intratumoural p‐TLS appeared to provide effective local tumour control and was generally well tolerated. This minimally invasive approach may represent a practical treatment option for equine melanoma, particularly where surgical management or referral‐based treatment is not feasible. However, these findings should be interpreted with caution because of the small sample size, absence of a control group and variable follow‐up duration.