🖤 Vet’s 2025 Guide to Equine Melanoma in Horses

By Dr Duncan Houston BVSc

1. What Is Equine Melanoma?

Equine melanoma arises from uncontrolled growth of melanocytes and is the third most common skin cancer in horses after sarcoids and squamous-cell carcinoma :contentReference[oaicite:3]{index=3}. It’s especially prevalent in grey horses, with ~80% developing at least one tumor by age 15 :contentReference[oaicite:4]{index=4}. Many are benign, but malignancy can occur and cause local or internal spread :contentReference[oaicite:5]{index=5}.

2. Types of Equine Melanoma

• Melanocytic nevus: small, benign nodules in young horses (<2 yrs) :contentReference[oaicite:6]{index=6}.
• Dermal melanoma: typically benign, seen in mature grey horses, often around tail docking site :contentReference[oaicite:7]{index=7}.
• Dermal melanomatosis: multiple coalescing tumors; higher metastatic risk :contentReference[oaicite:8]{index=8}.
• Anaplastic/malignant melanoma: rare, aggressive, often in non-grey horses :contentReference[oaicite:9]{index=9}.

3. Common Locations & Clinical Signs

Typical tumor sites include under the tail, around the anus and prepuce, eyelids, lips, throatlatch and parotid region :contentReference[oaicite:10]{index=10}. Signs can include masses that ulcerate, discharge dense black fluid, cause colic or defecatory issues when located near genital or anal regions :contentReference[oaicite:11]{index=11}.

4. Why Grey Horses Are Prone

Grey horses carry a dominant STX17 gene mutation linked to gradual depigmentation and melanoma risk :contentReference[oaicite:12]{index=12}. Up to 66% of these melanomas may eventually metastasize :contentReference[oaicite:13]{index=13}, although rates vary between studies :contentReference[oaicite:14]{index=14}.

5. Diagnosing Melanoma

• Clinical exam: palpation and appearance of pigment nodules.
• Fine needle aspiration or biopsy: helps confirm type and assess malignancy :contentReference[oaicite:15]{index=15}.
• Ultrasound/rectal exam: screens for internal spread :contentReference[oaicite:16]{index=16}.

6. Treatment Choices

Management depends on tumor size, location, and metastasis risk :contentReference[oaicite:17]{index=17}:

• Surgical excision: first-line for accessible masses; ~93% control rate :contentReference[oaicite:18]{index=18}.
• Cryotherapy or laser ablation: effective for small tumors; limited recurrence :contentReference[oaicite:19]{index=19}.
• Intralesional chemotherapy (cisplatin): often used with surgery; good efficacy :contentReference[oaicite:20]{index=20}.
• Immunotherapy (vaccine/DNA plasmid): promising but less effective (39% response rate); off-label canine vaccine (ONCEPT®) used experimentally :contentReference[oaicite:21]{index=21}.
• New heat-based therapy: non-invasive hyperthermia plus intratumoral chemo at RVC for inoperable sites :contentReference[oaicite:22]{index=22}.

7. Prognosis & Monitoring

Horses with benign or small tumors have excellent long‑term outlook :contentReference[oaicite:23]{index=23}. Advanced or metastatic cases carry guarded prognosis :contentReference[oaicite:24]{index=24}.

Regular monitoring every 6–12 months with imaging is vital for grey horses over 10 years old :contentReference[oaicite:25]{index=25}.

8. Prevention & Early Actions

• Annual screening, especially in grey horses.
• Early intervention of new or growing masses.
• Consider immunotherapy in high-risk areas.
• Document and photograph lesion growth patterns.

9. Ask A Vet Integration 🩺

At Ask A Vet, we provide telehealth support—helping owners with lesion monitoring plans, arranging diagnostics, treatment coordination, immunotherapy advice, and schedule follow-ups. Our app allows remote assessment of lesions with image guidance and priority access to oncology referrals. Download the Ask A Vet app today for expert melanoma care in 2025!

10. Quick‑View Treatment Table

11. FAQs

❓ Should I treat every melanoma?

No—small, benign lesions can be monitored. Treat if they grow, ulcerate, or impair function.

❓ Is melanoma life-shortening?

Not necessarily—many grey horses live normally with small tumors. Widespread/metastatic disease has a guarded prognosis.

❓ Is immunotherapy effective?

There's evidence of tumor shrinkage, but responses vary. Immunotherapy is best used alongside other treatments :contentReference[oaicite:26]{index=26}.

12. Final Thoughts

Equine melanoma, especially in grey horses, is common and often benign—but early detection and appropriate management are key to maintaining health and comfort. Surgical removal of accessible lesions, intralesional chemotherapy, and emerging therapies offer effective results. Combined with regular screening, owner education, and telehealth support from Ask A Vet, your horse can thrive even with melanoma. Download the Ask A Vet app now for expert guidance, monitoring tools, and compassionate oncology support in 2025 and beyond. ❤️