Intratumoral para-toluenesulfonamide as a tumor-ablative therapy for equine cutaneous tumors: a case series of three horses.

Equine neoplasia, including sarcoids, melanomas, and squamous cell carcinomas, presents therapeutic challenges due to recurrence and limitations of conventional treatments. Para-toluenesulfonamide (p-TLS) is a tumor-ablating agent that is associated with localized tumor necrosis and subsequent lesion resolution. It has been evaluated in human clinical settings as an intratumoral treatment of malignant airway obstruction caused by non-small cell lung cancer. This study aimed to describe the clinical outcomes and tolerability of intratumoral p-TLS in equine neoplasia. Three equine cases, including a fibroblastic sarcoid, perianal melanoma, and penile squamous cell carcinoma, were treated. The fibroblastic sarcoid and penile squamous cell carcinoma achieved complete response. The melanoma fulfilled the criteria for partial response at the protocol-defined clinical evaluation timepoint and subsequently demonstrated complete clinical resolution during follow-up. All cases demonstrated a consistent pattern of response characterized by tumor necrosis, sloughing, and subsequent wound healing with complete re-epithelialization. Local adverse effects were limited to transient inflammation and mild discomfort, which were effectively managed with supportive care. No severe adverse events or tumor recurrence were observed during the follow-up period ranging from 120 days to 15 months. These findings suggest that p-TLS may represent a feasible, highly minimally invasive intratumoral therapeutic approach for equine neoplasia and support further evaluation.