Clinical outcomes of intratumoural para‐toluenesulfonamide treatment in equine melanoma

Equine melanoma is one of the most common cutaneous neoplasms in horses and is particularly prevalent in grey horses. Although these tumours often exhibit slow growth, they may still demonstrate progressive or locally invasive behaviour, which can make treatment decisions challenging in clinical practice. This study 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 their home premises between June 2023 and November 2025. Tumour response was assessed based on clinical examination, tumour measurements and serial photographic documentation. Follow-up was obtained through veterinary re-examination or owner-reported communication. Complete response was achieved in six of seven horses (85.7%), while one horse showed partial response. Local tumour necrosis and sloughing were observed in all cases, followed by wound healing. Mild adverse effects, including local inflammation and transient systemic signs, were noted 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 in this small case series and was well tolerated under field conditions. This approach may represent a practical treatment option for equine melanoma, particularly in cases where surgical management is not feasible.