⚠️ Vet’s 2025 Guide to Equine Squamous Cell Carcinoma (SCC)

By Dr Duncan Houston BVSc

1. What Is Equine SCC?

Squamous cell carcinoma (SCC) is a malignant tumor arising from squamous epithelial cells. In horses, it’s the second most common skin cancer, frequently affecting areas with minimal pigment—especially around the eyes, genital region, and mucocutaneous junctions :contentReference[oaicite:3]{index=3}.

2. Why Owners Should Care

• Locally invasive and may metastasize to lymph nodes or internal organs.
• Risk factor for paraneoplastic hypercalcemia, which can lead to systemic illness :contentReference[oaicite:4]{index=4}.
• Animals may suffer from pain, ulceration, and functional impairment (e.g., eye irritation, colic).

3. Who Is at Risk?

• Unpigmented horses—Appaloosas, Paints, grey horses with pale skin.
• High UV exposure—stallions, mares, geldings with white eyelids or genital skin.
• Chronic irritation—flies, smegma buildup, papillomavirus infection (EcPV2) are implicated, especially in penile SCC :contentReference[oaicite:5]{index=5}.

4. Recognising Clinical Signs

• Pink cauliflower-like or ulcerated mass—commonly on eyelids, conjunctiva, genital regions :contentReference[oaicite:6]{index=6}.
• Chronic discharge, bleeding, swelling, and visible lymph node enlargement.
• Systemic signs may include weight loss and, in rare cases, hypercalcemia.

5. Diagnosing SCC

• Clinical exam: thorough physical check of eye, eyelids, penis, vulva, mouth.
• Biopsy or FNA: confirms diagnosis and checks for local invasion or malignancy.
• Imaging: ultrasound of lymph nodes; ocular ultrasound for eye masses.
• Bloodwork: check calcium levels if systemic signs are present :contentReference[oaicite:7]{index=7}.

6. Treatment Options

Treatment depends on location, tumor size, and metastasis:

• Surgical excision: mainstay therapy—aims for clean margins; may require complex reconstruction.
• Cryotherapy or laser ablation: cryogenic freezing or CO₂ laser for small lesions, especially on eyelids :contentReference[oaicite:8]{index=8}.
• Intralesional chemotherapy: cisplatin injections often combined with surgery.
• Radiation therapy: strontium plesiotherapy ideal for periocular lesions; HDR brachytherapy used for complex locations :contentReference[oaicite:9]{index=9}.
• Immunotherapy: experimental use of liposomal TLR agonists shows 67% response in ocular SCC :contentReference[oaicite:10]{index=10}.
• Supportive care: pain relief, fly control, ulcer management, lymph node monitoring.

7. Prognosis & Follow-Up

• Early excision: excellent prognosis with low recurrence.
• Large or invasive masses: guarded prognosis due to local spread or possible metastasis.
• Regular rechecks every 3–6 months, including examination of local lymph nodes and bloodwork.

8. Prevention Strategies

• Use UV-blocking flymasks, sunblock on eyelids, and shade to protect sensitive skin.
• Maintain hygiene: clean genital areas regularly to prevent smegma buildup.
• Promptly biopsy any suspicious lesion.

9. Case Study

A grey Quarter Horse mare developed a 1 cm ulcerated mass on her lower eyelid. Biopsy confirmed SCC. She received surgical excision + cryotherapy and anti-inflammatory topical medications. The tumor resolved with no recurrence at 12 months.

10. Ask A Vet Integration 🩺

At Ask A Vet, we guide owners through lesion assessment via app photos, treatment planning, arranging specialist referrals (surgery, oncology), providing telehealth check-ins, and coordinating follow-up care. For ocular or genital masses, our app offers direct access to specialists and tailored protocols. Download the Ask A Vet app today for early detection and expert SCC support! ❤️

11. Quick Reference Table

12. FAQs

❓ Is every pink mass SCC?

No—nodules may include granuloma, papilloma, sarcoid, or melanoma. Biopsy is essential.

❓ Can SCC metastasise?

Yes—especially larger tumors or those untreated; lymph nodes are common metastasis sites.

❓ Is radiation safe?

Yes—local radiation therapies are generally effective with minimal side effects.

13. Final Takeaways

Squamous cell carcinoma is common in unpigmented areas of horses and demands early detection and aggressive treatment. With surgical removal, cryotherapy, radiation, or evolving immunotherapies, many horses recover well. Ongoing surveillance and skin care are crucial. Ask A Vet connects you with specialists early, aiding treatment planning and long-term monitoring. Download our app now to protect your horse’s health in 2025 and beyond! ❤️