Squamous Cell Carcinoma in a Horse’s Eyelid – Vet Guide 2025 🐴👁️

By Dr Duncan Houston, BVSc

Introduction

Squamous cell carcinoma (SCC) is the most common tumor affecting the horse’s eyelid, cornea, or third eyelid—a malignancy akin to “cancer eye” in cattle. White or light-pigmented skin around the eye, frequent UV exposure, and genetic predisposition elevate risk, especially in breeds like Appaloosas, Haflingers, Belgians, and warmbloods :contentReference[oaicite:2]{index=2}.

Why Vigilance is Key

• Early SCC appears as a small red bump or inflamed area, easily confused with conjunctivitis or allergies :contentReference[oaicite:3]{index=3}.
• If untreated, SCC can rapidly grow, covering eyelids or cornea, invade deeper tissues, or even metastasize :contentReference[oaicite:4]{index=4}.
• A biopsy is essential to distinguish SCC from infection, dust irritation, or other tumors :contentReference[oaicite:5]{index=5}.

Predisposing Factors

• Lack of pigment around the eye: Horses with white eyelids or faces are particularly vulnerable :contentReference[oaicite:6]{index=6}.
• UV exposure: Higher elevations or sunny climates increase SCC risk :contentReference[oaicite:7]{index=7}.
• Genetics: DNA link identified in Haflingers, Belgians, and Rocky Mountain Horses :contentReference[oaicite:8]{index=8}.
• Age & chronic irritation: Older horses and chronic wounds contribute to tumor development :contentReference[oaicite:9]{index=9}.

Clinical Signs to Watch

• Raised pink or red mass on eyelid, limbus, conjunctiva, or third eyelid :contentReference[oaicite:10]{index=10}.
• Mild tearing in one eye, mimicking allergies or conjunctivitis :contentReference[oaicite:11]{index=11}.
• Ulceration, scabbing, intermittent bleeding, discharge :contentReference[oaicite:12]{index=12}.
• In advanced cases: distortion of eyelid, facial swelling, potential loss of orbital integrity :contentReference[oaicite:13]{index=13}.

Diagnosis

Diagnosis begins with clinical suspicion and must be confirmed via biopsy and histopathology. Definitive diagnosis distinguishes SCC from similar lesions like summer sores or sarcoids :contentReference[oaicite:14]{index=14}.

Treatment Options

Treatment depends on tumor size, location, and depth:

1. Surgical Excision

• Primary treatment for small, well-defined eyelid tumors.
• Wide margins necessary; may require eyelid reconstruction :contentReference[oaicite:15]{index=15}.
• Recurrence rates up to 80% if done alone :contentReference[oaicite:16]{index=16}.

2. Adjunctive Therapies

• Intralesional 5‑fluorouracil (5‑FU): Oklahoma State study in five horses showed tumor reduction, allowing subsequent removal :contentReference[oaicite:17]{index=17}.
• Topical/intralesional chemo: Cisplatin, carboplatin, mitomycin C :contentReference[oaicite:18]{index=18}.
• Cryotherapy: Freezes small lesions; effective but depth-limited :contentReference[oaicite:19]{index=19}.
• Radiation therapy: Gamma or beta radiation reduces recurrence to 10–15% :contentReference[oaicite:20]{index=20}.
• Photodynamic therapy & hyperthermia: Use photosensitive agents and heat to ablate tumors :contentReference[oaicite:21]{index=21}.
• Enucleation: Invasive or recurring tumors may require eye removal for pain relief and cure :contentReference[oaicite:22]{index=22}.

Prognosis

• Early diagnosis + combined therapy often results in successful treatment and eye preservation :contentReference[oaicite:23]{index=23}.
• Large or bone-invading tumors have a guarded to poor prognosis :contentReference[oaicite:24]{index=24}.
• Recurrence possible even after treatment; annual eye exams recommended for high-risk horses :contentReference[oaicite:25]{index=25}.

Prevention & Owner Actions

• UV protection: Use UV-blocking fly masks and provide shade during midday sun :contentReference[oaicite:26]{index=26}.
• Genetic testing: Especially recommended for Haflingers, Belgians, and Rocky Mountain Horses :contentReference[oaicite:27]{index=27}.
• Regular eye checks: Look for small red bumps or asymmetrical tearing.
• Contact your vet immediately for any persistent or atypical lesions.

Case Study Highlight

In the Oklahoma State study, intralesional 5‑FU was administered to five horses with eyelid SCC. Tumors shrank significantly—while not a cure, it reduced size to enable surgical removal or other therapy :contentReference[oaicite:28]{index=28}.

Conclusion

Squamous cell carcinoma of the eyelid is a serious yet treatable condition if caught early. Owners of light-pigmented or high-risk breeds must stay vigilant. Any suspicious ocular lesion demands veterinary evaluation, biopsy, and often combined therapy. With prompt action, vision and well-being can often be preserved.

See a bump or persistent tearing? Reach out to Ask A Vet via AskAVet.com or our app for expert guidance, photo triage, and bespoke treatment planning. 🩺📱