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What Is That Black Mole on My Dog's Leg?

Adrienne is a certified dog trainer, behavior consultant, former veterinarian assistant and author of Brain Training for Dogs.

Black mole on dog's leg: dome-shaped melanocytoma.

Black mole on dog's leg: dome-shaped melanocytoma.

In the article below, you'll find:

  1. What to do if you find a black mole on your dog's leg or foot.
  2. A brief overview of dog moles.
  3. A definition of melanocytomas.
  4. A video tutorial about melanoma and what you need to know about cancer in dogs.
  5. A reader survey and a list of articles on this topic.
Kaiser's melanocytoma is slightly pedunculated.

Kaiser's melanocytoma is slightly pedunculated.

I Just Found a Black Mole on My Dogs' Legs

Did you find a small, black mole on your dog's leg? If so, you are not alone.

While grooming, I found a shiny, black mole on my female Rottweiler's leg the other day, and one on my male's leg a few months earlier. I am a big advocate for grooming. It is much more than just removing dead hairs from your dog's coat. If your dog loves to be groomed (which he should, if you got him used to it from an early age), it's a great opportunity to bond, spend time together, pamper your dog, and take notice of any unusual lumps, bumps, or moles your dog develops in a timely manner. As in humans, any suspicious lumps, bumps or moles should always be seen by your veterinarian.

The moles were overall small. My female's is about the size of a sesame seed, my male's about the size of the tip of a pencil eraser. In both dogs they were nearby their wrist area in their front legs. I found it odd that they both had it in the almost same exact spots and that both moles looked almost the same. Perhaps it's because they're litter mates?

I scheduled a vet appointment to make sure it was nothing serious. Before heading to the vet, I did some research. I always conduct research before vet appointments, not because I am hoping to diagnose my dogs myself, but so I can prepare questions to ask and have a general idea what to expect.

Are Dogs' Moles Dangerous?

What are moles? Moles are small bumps that are typically brown, black or bluish. Their characteristic dark color is caused by a pigment present in the body's cells known as melanin. Melanin is what gives you than nice, dark tan after staying in the sun. Growths with presence of melanin are known as melanocytic tumors. These growths are more common in heavily pigmented animals.

As in humans, moles in dogs may in most cases be benign, but there are always those chances of them occasionally being malignant. However, unlike humans, where the effect of the sun plays a primary role in the growth of moles, in animals, solar damage is seldom associated with the development of melanocytic tumors, according to the Merck Veterinary Manual.

It's important to always have any suspicious lumps, bumps or moles checked out by the vet. Especially when you first notice them. Mast cell tumors, for instance, are cancers that behave erratically and can assume even benign looking forms. Some times they can grow, then shrink, then grow again and they may appear red but sometimes even dark ad hyper-pigmented.

And even when the vet confirms the mole is nothing to worry about, it's always a good idea to keep an eye on it and report to the vet if the mole grows quickly in size or becomes irritated, red or starts oozing pus or blood which is a sign of an abundance of blood vessels. It's important to keep an eye on the margins as well.

In my dog's case, both moles turned out being benign tumors. I asked my vet exactly what kind or growths they were and she confirmed what I had thought after reading about them. She told me they both were likely melanocytomas and that for now we can just keep a watchful eye on them.

What Are Melanocytomas?

Also known as "benign melanoma", this type of mole is caused by benign accumulations of melanocytes. The pre-fix "melano" refers to melanin-producing cells while the suffix word "cytoma" means tumor of the cell. In most cases, the suffix "-oma" is added to the tissue of origin to mean it's a benign tumor. For instance, fibroblasts – fibroma, bone – osteoma, cartilage – chondroma, blood vessels – hemangioma.

Which dogs are predisposed? According to the National Canine Foundation, melanocytomas are more common in older dogs with darkly pigmented skin. They are often found in areas of haired skin or in the mouth. They're commonly found in dogs between 5 and 11 years of age with a predilection for dogs belonging to the following breeds: Vizsla, Miniature and Standard Schnauzer, Doberman Pinscher, Airedale Terrier, Golden Retriever and Irish Setters. According to the Merck Veterinary Manual, they are often found on the head and forelimbs of middle-aged or older dogs and are more prevalent in male dogs.

What do they look like? Melanocytomas present as small, pigmented macules (generally measuring from one-quarter to 2 inches in diameter) that are generally black, but can also be different shades of brown, gray and red. This is the tumor the vet diagnosed my dogs with both times and is seen in the pictures. Here are more pictures from Just Answer: Dog Black mole 1 and dog black mole 2. Even though these are benign growths, the vet said to keep an eye on them for any changes.

How do they behave? According to Philip J. Bergman, a veterinarian specializing in oncology, melanomas found in areas of haired-skin that are not in proximity to mucosal margins (lips, mouth) tend to behave in a benign manner. Yet, he explains how sometimes you may stumble on a melanoma that engages in an unreliable biologic behavior.

For this reason, biopsy of benign melanomas in dogs is recommended for the simple fact that a pigmented mass can also be indicative of melanocytic hyperplasia, hemangioma, hemangiosarcoma, basal cell tumor, or histiocytic sarcoma. While it's true that location is often indicative of whether a melanoma is benign or malignant, according to a 2011 paper by Elizabeth Downing for Cornell University College of Veterinary Medicine about 80% of tumors found in areas of haired skin are benign while 20% are malignant. The paper presents a case where a pigmented growth on the skin of a dog turned out being a malignant melanoma, despite the fact it was in the dog's left lumbar region.

Generally, according to the paper, benign melanomas are firm, but mobile over the underlying tissues, well defined, measure less than 2 centimeters, and their mitotic index (the ratio of the number of cells that are undergoing cell division to the number that are not ) is less than 3 per 10 HPF. Malignant melanomas, on the other hand tend to grow rapidly, extend into underlying tissues,are larger t than 2 centimeters, tend to ulcerate and have a mitotic index greater than 3 per 10 HPF. Yet, another paper further suggests that other studies demonstrated that behavior of melanomas wasn't always correlated with their histologic appearance in 10 to 40% of histologically benign oral and cutaneous canine melanoma.

Note: melanomas found in the dog's mouth, lips or toenail bed are usually highly malignant, explains veterinary surgeon Dr. Daniel A. Degner.

So Are Moles Dangerous or Not?

Even though my vet was comfortable telling me to keep an eye on the area due to its size, appearance, and location, my take-home message is that even benign-looking growths (like benign melanocytomas) may behave in unpredictable manners.

Most vets adhere to the "when you hear hoofs, think horses not zebras," but the truth is nobody wants to open the door and find a black striped beast that goes by the name of cancer. So to play it safe, I feel it never hurts to seek another opinion. I let my dogs see another vet just to be safe, and she confirmed they look benign, but she thinks a biopsy won't hurt and since they're due soon for their dental cleaning soon, they might just nip those growths off to play it safe.

Update: Recently, my male dog's moles appear to be enlarged. It's no longer flat like a skin tag but sort of swollen like a raisin. He has also been licking it lately, but I'm not sure if he's licking it because it's enlarged or if it's enlarged because of the licking.

The vet palpated it and noticed it was bleeding slightly. She recommended removing it and having it biopsied "as sometimes they behave in a concerning way."

After the pathology report arrived, my vet said: "Remember how I told you that sometimes moles behave in a concerning way? Turns out it was a melanoma." She added that it's unlikely to grow back and to just keep an eye that he doesn't ever grow any in his mouth or by the toes as those are where these growths have a poor prognosis.

Disclaimer: This article is not to be used as a substitute for veterinary advice. If you find a black mole on your dog, please see your vet.

Melanoma - What You Need to Know About Your Dog's Cancer

Four further reading

  • Signs of Osteosarcoma (Bone Cancer) in Dogs
    Learn more about the signs of osteosarcoma, bone cancer in dogs affecting the legs. Please see your vet if you notice any limping and or suspicious swellings in your dog's legs.
  • Canine Soft-Tissue Sarcomas in Dogs
    Among the variety of neoplasias found in dogs, soft-tissue sarcomas are quite common. Learn more about this type of cancer and how it affects dogs.
  • Are Dog Lipomas Cancerous?
    If your suspect your dog has a lipoma or your vet diagnosed a lipoma in your dog, you may wonder if it is cancerous. While lipomas are for the most part benign, learn to recognize potential risks.
  • Dog Wart Removal Using Thuja
    Looking for a dog wart home remedy? Many dog owners have been having success with thuja for dogs warts. Of course, always consult with a vet before trying home remedies or natural remedies.
  • My Dog Has a Lump What Is It?
    So you found a lump on your dog and you are wondering what it may be. Look no further as there can be various causes of such a lump. We will see why it's so important to have it checked out.
  • Causes of Lumps and Masses in the Mouth in Dogs
    What causes unusual growths in the dogs dog's mouth? There are several causes for growths, lumps and masses in the dog's mouth and all of them should be investigated by your vet.
  • Causes of Lumps on Dog Paw Pads
    Wondering what may cause unusual lumps and bumps on a dog's paw pad? Learn possible causes for why your dog has lump on paw pad and why it's so important to see the vet.

This article is accurate and true to the best of the author’s knowledge. It is not meant to substitute for diagnosis, prognosis, treatment, prescription, or formal and individualized advice from a veterinary medical professional. Animals exhibiting signs and symptoms of distress should be seen by a veterinarian immediately.

Questions & Answers

Question: My Russel has two wart like growths that are mostly pink with a little black and are bumpy. What are they?

Answer: Most lumps and bumps will need a vet to take a look at and possibly do a very inexpensive test called Fine Needle Aspiration. A small needle is used to aspirate a few cells from the growth. This is not a painful procedure and does not require anesthesia. Once the cells are aspirated, they are then smeared on a slide and stained for viewing under the microscope. This will help the vet have a better idea of what you may be dealing with. Any lumps and bumps need to be checked out because some forms of cancer may mimic innocent looking warts. For example, mast cell tumors are known as the "great imitator" because it can take many forms.

Comments

Adrienne Farricelli (author) on March 10, 2020:

Hi Emily, keep us posted on what it turns out to be, hopefully it's nothing serious.

Emily on March 08, 2020:

My almost 5 year old Labrador (He will be 5 in a few weeks) has a black lump on his rear leg up near his bum , it's not very big and I am keeping an eye on it and planning to show it to the vet on our next appointment (he always seems to find ways to see the vet just recently) . At first it looked like a tick but after careful examination it is a lump and I am unsure as to what it is. I only saw it a couple of days ago but how quickly do they grow? Just so I can keep track of it I've been taking pictures of it but so far I haven't seen any big changes in its growth.

Adrienne Farricelli (author) on April 18, 2018:

Francesca, my vet had my dog's mole surgically removed.

Francesca on May 10, 2017:

Since your dog had melanin, what was the cure?

Adrienne Farricelli (author) on September 05, 2015:

Thanks for catching that Maggie, I initially was talking about melanin in the first chapters, and not sure how I ended up talking about melatonin, maybe because I haven't had enough sleep and would have benefited from some, lol!

maggie on September 05, 2015:

Melanin is what gives pigment to skin and is found in skin growths. Melatonin is supplement you can take to help you sleep