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

Overview

• This study evaluated the use of para-toluenesulfonamide (p-TLS), a tumor-ablating agent, as an intratumoral treatment for different types of cutaneous tumors in horses.
• The treatment showed promising results, including complete responses in two cases and partial followed by complete resolution in one case, with manageable side effects and no tumor recurrence observed during follow-up.

Background and Rationale

• Equine cutaneous tumors such as sarcoids, melanomas, and squamous cell carcinomas often have high recurrence rates and present challenges to conventional treatments.
• Para-toluenesulfonamide (p-TLS) is known as a tumor-ablating agent that induces localized tumor necrosis, leading to lesion resolution.
• p-TLS has been previously tested in humans for malignant airway obstructions linked to non-small cell lung cancer, demonstrating potential for tumor control via intratumoral injection.
• This study aimed to assess the clinical outcomes, safety, and tolerability of intratumoral p-TLS in horses with naturally occurring tumors.

Case Series and Treatment Approach

• Three horses presenting with different tumor types were included:
  • One with fibroblastic sarcoid
  • One with perianal melanoma
  • One with penile squamous cell carcinoma
• The tumors were treated by direct intratumoral injection of p-TLS, aiming for localized ablation of tumor cells.

Clinical Outcomes

• Fibroblastic sarcoid and penile squamous cell carcinoma cases:
  • Both cases showed complete tumor response, meaning the tumors fully resolved clinically.
• Perianal melanoma case:
  • Initially met criteria for a partial response during the immediate clinical evaluation.
  • Showed complete clinical resolution during longer-term follow-up.
• The typical response pattern in all cases involved:
  • Tumor necrosis after injection
  • Subsequent sloughing off of necrotic tumor tissue
  • Healing with complete re-epithelialization of the lesion site

Safety and Tolerability

• All horses tolerated treatment well.
• Adverse effects were limited to:
  • Transient localized inflammation
  • Mild discomfort, which was manageable with supportive care
• No severe adverse events were reported.
• Importantly, no tumor recurrence was observed during follow-up periods ranging from 120 days to 15 months.

Conclusions and Implications

• Para-toluenesulfonamide (p-TLS) shows promise as a minimally invasive, intratumoral therapy for treating equine cutaneous tumors.
• The case series demonstrated effective tumor ablation and healing with an acceptable safety profile.
• This therapeutic approach may be particularly useful where conventional treatments are limited or tumor recurrence is problematic.
• The study supports further larger-scale evaluations to validate efficacy and safety across more cases and diverse tumor types.