🧬 Vet Guide 2025: Malignant Melanoma in Dogs and Cats – Diagnosis, Danger Zones & Advanced Treatments 🐾

By Dr Duncan Houston, BVSc

Malignant melanoma is a serious form of cancer affecting pigment-producing cells (melanocytes) in dogs and cats. While often associated with sun exposure in humans, in pets, this cancer most commonly affects the mouth, toes, and eyes—and is not usually linked to sun damage. In this 2025 vet guide, we’ll explore the types of melanoma, where they occur, how to diagnose and stage them, and what advanced treatment options are available. 🐶🐱

🔬 What Is Malignant Melanoma?

Melanoma is a tumor of melanocytes, the cells that produce pigment (melanin). It can appear as a dark mass or ulcerated lesion. While many skin melanomas in pets are benign, tumors in specific areas tend to be more dangerous. These include:

• 👄 Mouth and lips
• 🐾 Toes (digits)
• 👁️ Eyes

Melanomas in these “danger zones” often behave aggressively and may metastasize (spread) to the lungs, liver, lymph nodes, and beyond. 🎯

🟤 Benign vs. Malignant Melanomas

Skin-based melanomas (on haired areas):

• ✅ Often benign
• 🔬 May look malignant under the microscope but behave harmlessly
• 📏 Mitotic index (number of dividing cells) helps predict behavior

Melanomas near mucosal margins (mouth, genitals):

• ⚠️ More likely to be malignant
• 🧪 Biopsy and tissue staining (e.g., Ki-67) help assess aggressiveness

📍 High-Risk Melanoma Locations

1️⃣ Oral Melanoma (Mouth, Lips, Gums)

• 🚨 Highly malignant and invasive
• 🦷 Destroys oral tissue and bones
• 📈 Spreads quickly to lungs and lymph nodes

Staging system (World Health Organization):

• Stage I: Tumor < 2 cm — survival ~17–18 months
• Stage II: Tumor 2–4 cm — survival ~6 months
• Stage III: Tumor > 4 cm or lymph node involvement — survival ~3 months
• Stage IV: Distant metastasis — survival ~1 month

2️⃣ Toe/Digit Melanoma

• 🖤 Often mistaken for infected toenail or swelling
• 🔍 Usually requires toe amputation for diagnosis
• 📉 Median survival ~1 year post-amputation

3️⃣ Eye Melanoma

Dogs:

• 👁️ Uveal melanomas are benign in 80% of cases
• ⚠️ Still cause pain or glaucoma; may require eye removal (enucleation)

Cats:

• 🧬 60–70% are malignant and likely to spread
• 🧪 Flat iris pigmentation may signal early melanoma (or benign iris melanosis)

4️⃣ Epibulbar Melanoma (Outer Eye Surface)

• 🩺 Usually benign in cats and dogs
• ✅ Treatable with surgery, laser, or cryotherapy

🧪 Diagnosing & Staging Melanoma

• 🔬 Biopsy: Confirms tumor type and malignancy
• 📸 Chest X-rays: Check for spread to lungs
• 🧫 Lymph node aspiration: Detect microscopic spread
• 🖥️ Abdominal ultrasound: Screens internal organs

Staging is essential for creating a treatment plan and estimating prognosis. 🎯

💊 Treatment Options

1️⃣ Local Disease Control

• ✂️ Surgery – best option if margins are clear
• 💥 Radiation – useful if tumor cannot be fully removed

2️⃣ Distant Disease Control

• 💉 Chemotherapy – used when spread is confirmed
• 💊 Carboplatin + Piroxicam – shown to extend survival in Stage IV

3️⃣ Microscopic Disease Control

• 🧬 Immunotherapy – stimulates immune system to attack remaining cancer cells

💉 The Melanoma Vaccine

• 💉 Uses human tyrosinase to trick the immune system into attacking melanoma cells
• 🗓️ Given in 4 doses (every 2 weeks), then boosters every 6 months
• 🎯 Effective for oral and toe melanomas after surgical removal
• 📉 Not helpful once distant metastasis is present

Available only through veterinary oncologists. It’s not preventative, but therapeutic. ✅

📲 Ask A Vet for Cancer Support

Worried about a dark lump in your pet’s mouth or foot? Suspect a melanoma diagnosis? Connect with AskAVet.com to speak with a veterinary professional any time. 🩺

With the Ask A Vet App, you can:

• 📸 Upload images of suspicious growths
• 📅 Ask about biopsy, staging, and treatment timelines
• 💬 Discuss melanoma vaccine eligibility

📝 Final Thoughts

Malignant melanoma is a serious and fast-moving cancer in pets—but treatment options continue to expand. Early detection, surgical intervention, and advanced tools like the melanoma vaccine offer hope for extended survival and improved quality of life. 🐾

If you suspect a melanoma, don’t wait. Reach out to your vet or connect with AskAVet.com for help navigating diagnosis and care. 🐶🐱