Melanocytoma in Dogs: What It Is and What Comes Next

A melanocytoma is a benign tumor of melanocytes, the cells that make pigment. In dogs, the term is used for benign melanocytic tumors of the skin, while "malignant melanoma" is used for cancerous ones wherever they occur (Smedley et al., 2022). Melanocytomas are diagnosed much more often than malignant melanomas, and complete surgical removal of a skin melanocytoma is curative (Villalobos, 2024).

Skin melanocytomas are usually dark, appear most often on the head and front legs, and tend to affect middle-aged or older dogs. Breeds at higher risk include Miniature and Standard Schnauzers, Doberman Pinschers, Golden Retrievers, Irish Setters, and Vizslas (Villalobos, 2024).

Melanocytomas also occur in the eye. Anterior uveal melanocytoma, inside the eye, is the most common tumor found in canine eyes submitted to one large pathology registry (Dubielzig, n.d.). These tumors rarely spread, but they can grow into nearby structures and cause glaucoma (de Vries & Stadler, 2025).

Location matters. A dark tumor on the lip, in the mouth, or in a nail bed is more likely to be malignant than one on the haired skin (Smedley et al., 2022), so any pigmented mass needs a biopsy rather than a guess.

Key points

• Melanocytomas are benign, and complete surgical removal of a skin melanocytoma is curative (Villalobos, 2024).
• They're far more common than malignant melanomas (Villalobos, 2024).
• Tumors in the nail bed, at the lip margin, and in the mouth generally have a worse prognosis than those on haired skin (Smedley et al., 2022).
• Pathologists use features such as mitotic count, nuclear atypia, pigmentation, and the Ki-67 index to separate benign from malignant tumors (Smedley et al., 2022).
• Eye melanocytomas rarely spread, but they can cause glaucoma, and removing the eye is often recommended (de Vries & Stadler, 2025).
• Breed affects risk but can't predict behavior on its own (Smedley et al., 2022).

Detailed explanation

What a melanocytoma looks like

On the skin, melanocytomas can appear as flat spots or patches, raised bumps or plaques, or raised masses that sometimes hang from a stalk. Most are pigmented, usually brown to black. They're generally single, though some dogs, especially at-risk breeds, develop more than one (Villalobos, 2024).

Malignant melanomas, by contrast, are typically raised nodules that are often ulcerated, and some have little or no pigment. They're most common at the lip margins, in the mouth, and in the nail beds (Villalobos, 2024). That overlap in appearance is why a dark lump can't be called benign just by looking. Our article on bumps on dogs covers other common lumps, lumps that aren't cancer explains the benign possibilities, and our 10-minute dog cancer check can help you track new ones.

Why location matters

Where a melanocytic tumor grows strongly affects how it behaves. Tumors in the nail bed, at the junction of skin and mucous membrane (such as the lips), and in the mouth generally carry a worse prognosis than tumors elsewhere on the skin. In one study, survival was longest for skin tumors, intermediate for nail bed and lip-margin tumors, and shortest for oral tumors (Smedley et al., 2022). Nail bed tumors tended to be malignant, while tumors on the skin of the belly were more often benign (Smedley et al., 2022).

Still, location isn't destiny. Malignant melanomas can occur on haired skin, and some oral tumors have low malignancy (Smedley et al., 2022). If your dog has a pigmented lesion on a toe, see our article on dog toe cancer. For tumors in the mouth, our page on squamous cell carcinoma in the mouth covers oral masses more broadly.

How a melanocytoma is diagnosed

A biopsy, reviewed by a pathologist, is how a melanocytoma is told apart from a melanoma. A 2022 review of canine melanocytic tumors describes the features pathologists weigh (Smedley et al., 2022):

• Mitotic count: how many cells are dividing. For skin tumors, a count of 3 or more is linked to shorter survival.
• Nuclear atypia: how abnormal the cell nuclei look. In skin tumors, more than 20% atypical nuclei suggests more aggressive behavior.
• Pigmentation: heavily pigmented tumors, with 50% or more pigmented cells, are linked to a better prognosis.
• Ki-67 index: a stain that measures how fast cells are growing. For skin tumors, 15% or more is linked to shorter survival, and in one study no benign skin tumor reached that level.
• Depth, thickness, and invasion of blood vessels: deeper, thicker tumors and those invading vessels behave more aggressively.

When the features don't clearly point one way, the pathologist may call the tumor a "melanocytic neoplasm" rather than a melanocytoma or a melanoma (Smedley et al., 2022). If your report uses that term, ask what features were seen and whether extra testing, such as Ki-67, would help. Our guides to reading a pathology report and what clear margins mean explain the terms you'll see.

Breed and risk

Some breeds are more likely to develop melanocytic tumors, but breed doesn't settle whether a tumor is benign. In Doberman Pinschers and Miniature Schnauzers, about 75% of melanocytic tumors behaved benignly, while in Miniature Poodles more than 85% behaved malignantly. Even so, breed alone isn't a reliable predictor (Smedley et al., 2022). Owners of Golden Retrievers and other at-risk breeds should have any new pigmented spot checked.

Melanocytomas of the eye

Inside the eye (anterior uveal melanocytoma). Melanocytic tumors of the iris and ciliary body are the most common primary tumors inside the canine eye, and most are benign melanocytomas (de Vries & Stadler, 2025). In one large ocular pathology database, there were 1,245 anterior uveal melanocytomas compared with 312 anterior uveal malignant melanomas (Dubielzig, n.d.). Melanocytomas are usually heavily pigmented, and spread to other parts of the body is reported in only a minority of cases. However, they often grow into nearby tissue, which can lead to glaucoma. The outlook for life expectancy is good, though removal of the eye is often recommended (de Vries & Stadler, 2025). Anterior uveal melanocytic tumors in dogs have a reported metastatic rate of about 5% (Oliver, 2012).

On the surface of the eye (limbal melanocytoma). These grow where the clear cornea meets the white of the eye. In the same database, the breeds most often affected were Labrador Retrievers, Golden Retrievers, and German Shepherds (Dubielzig, n.d.). Limbal melanocytic tumors tend to be benign but can grow quickly in young dogs. Monitoring can be appropriate for tumors that aren't growing, while surgical removal, often by a veterinary ophthalmologist and sometimes combined with laser or other therapies, is usually advised (Oliver, 2012).

A pigmented spot on or in the eye needs an exam by your veterinarian or a veterinary ophthalmologist. If your dog has a growth on the eyelid instead, our article on meibomian gland adenomas covers a common type of eyelid growth.

Treatment and outlook

For a skin melanocytoma, complete surgical removal is curative (Villalobos, 2024). If the margins are incomplete, ask your veterinarian whether a second surgery or monitoring makes more sense. Our article on recovery after cancer surgery covers aftercare.

If the biopsy instead shows a malignant melanoma, the plan changes. Malignant melanomas are locally aggressive with high potential to spread, though survival varies considerably (Villalobos, 2024). Our melanoma in dogs hub explains staging and treatment, and you may want to ask about a referral to a veterinary oncologist.

When to contact a veterinarian

Book an appointment soon if your dog has:

• A new dark spot or lump on the skin, or one that's changing in size, shape, or color
• Any pigmented mass on the lip, in the mouth, or around a nail
• A dark spot on the white of the eye or a change in the color of the iris

Call the same day if your dog has a painful, red, or cloudy eye, is squinting, or seems to have lost vision.

Questions to ask your veterinarian

• Can we biopsy this pigmented mass to tell whether it's a melanocytoma or a melanoma?
• What did the pathologist find for mitotic count, atypia, and Ki-67?
• Were the margins complete?
• Does the location of this tumor change its outlook?
• For an eye tumor, should we see a veterinary ophthalmologist, and is monitoring an option?
• How often should we check my dog for new spots?

Sources

de Vries, C., & Stadler, C. (2025). Dark spots in sight: Uveal melanocytic ocular tumours in dogs and cats. Laboklin. https://laboklin.com/wp-content/uploads/2025/07/Uveal_Melanocytic_Ocular_Tumours_Dogs-Cats.pdf

Dubielzig, R. R. (n.d.). Tumors of the canine globe [Presentation slides]. Comparative Ocular Pathology Laboratory of Wisconsin, University of Wisconsin-Madison School of Veterinary Medicine. https://www.vetmed.wisc.edu/lab/coplow/wp-content/uploads/sites/14/2023/03/CanineGlobeK92016.pdf

Oliver, J. (2012, July 2). Ocular melanomas in dogs and cats: Diagnosis and treatment. Vet Times. https://www.vettimes.com/clinical/small-animal/ocular-melanomas-in-dogs-and-cats-diagnosis-and-treatment

Smedley, R. C., Sebastian, K., & Kiupel, M. (2022). Diagnosis and prognosis of canine melanocytic neoplasms. Veterinary Sciences, 9(4), Article 175.

Villalobos, A. E. (2024). Tumors of melanocytic origin in animals. Merck Veterinary Manual, Professional Version. Retrieved November 10, 2026, from https://www.merckvetmanual.com/integumentary-system/tumors-of-the-skin-and-soft-tissues/tumors-of-melanocytic-origin-in-animals