Last Updated on September 20, 2023
You know what moles are, right? We call them beauty marks. These are roundish, sometimes slightly raised clusters of skin cells with darker pigmentation than the rest of your “normal” skin. They come in different shades of black, brown, gray, red, or pink. Their sizes can vary from as small as a quarter-inch to as large as 2 inches in diameter.
But what about dogs? Can dogs get moles like people, too? And are their moles anything to worry about?
What dog moles are like
Yes, dogs can have similar moles on their skin. Moles can appear anywhere — hidden underneath their fur, slightly jutting out the fur, or on the furless portions of their body. But dog moles do tend to appear on the forelimbs or head. (My own dog has a small brown mole on her left inner leg or “armpit.”)
And moles are harmless. They’re not something you should worry about. As previously mentioned, they are clusters (“macules”) of melanocytes or skin cells with more melanin or skin pigmentation. These melanocytes are benign and pose no threat to a dog’s overall health.
What causes moles to appear
It’s simple: moles pop up on the skins of dogs that are either of a certain age or are genetically predisposed to forming them.
Moles start appearing on adult dogs aged 5 to 11 years. Both males and females can form moles, but males tend to have them more often. Moles also tend to pop up in dogs from the following breeds (or those with a mix of the following breeds):
- Golden Retrievers
- Irish Setters
- Doberman Pinschers
- Schnauzers (both the standard and miniature breeds)
- Vizslas
- Airedale Terriers
Cancerous growths
However, just like humans, dogs can also develop skin cancer.
There are different types of canine skin cancer. Some of them come in forms that can look like moles.
Types of skin cancer that resemble moles
As in humans, dog skin has several layers. Skin cancer can emanate from any of these layers, forming distinct or “signature” tumors per type. At first glance, these tumors may look like moles.
1. Carcinoma
Squamous cell carcinomas are malignant tumors that first appear as raised lumps or patches on the skin. These typically pop up on a dog’s abdomen, but can also show up on a dog’s rear end, lower legs, or head. Carcinomas also tend to appear in older dogs and dogs of certain breeds, such as Poodles, Basset Hounds, and Bloodhounds.
Newly-formed carcinomas can be tricky to identify because they closely resemble moles and appear in roughly the same areas of a dog’s body. The only differences are that carcinomas feel firmer to the touch, and will change in both size and shape in a matter of days or weeks.
2. Malignant melanomas
Again, a mole is technically a benign melanoma. Melanomas are made up of melanocytes, which are skin pigment-producing cells. But occasionally, melanocytes can mutate and form malignant melanomas instead.
Veterinarians have observed that dogs from the Scottish Terrier and Schnauzer breeds (both miniature or standard) seem to form malignant melanomas more often than others. These malignant growths can also look like moles when they first appear. But unlike benign moles, these tend to form in places where moles don’t appear — like on a dog’s lips and gums, or in between toes and nails (i.e. nail beds). These come in various shades, from dark black or grey to pink or nearly colorless. They can grow into bulbous forms within a few weeks or months.
Sometimes, malignant melanomas that pop up in a dog’s toe or nail bed will even cause a bacterial infection that can mask or hide the true nature of the growth.
3. Malignant cutaneous histiocytomas
Histiocytes are a type of cell produced from bone marrow. These cells are part of the macrophages (those cells that devour foreign microbes and other harmful pathogens) in a dog’s immune system.
Histiocytes can form lumps or growths anywhere in a dog’s body (i.e., specific internal organs). Sometimes, they can also form tumors underneath or along a dog’s skin. Called cutaneous histiocytomas, these growths are usually benign. Over time, they are eliminated by the dog’s immune system.
However, there are rare occasions when cutaneous histiocytomas can become malignant cell tumors, and quickly metastasize towards the nearest lymph node.
Important Note: There are other types of skin cancer (such as mast cell tumors or fibrosarcomas) that don’t resemble moles, but which you also need to watch out for. Ask your vet to describe how these other cancers might look when they first appear anywhere in your dog’s body.
Why cancerous “moles” form
The biggest reason why these skin cancers form seems to be also genetics. If a dog is of a certain breed or family that has a history of forming cancerous skin tumors, there’s an increased chance that he, too, will experience the same.
But while some dogs may be predisposed to forming tumors, other factors are involved. Like humans, dogs can develop skin cancer if they are exposed to too much sun or harmful chemicals.
The National Canine Cancer Foundation also believes that some skin cancers or cell mutations can be brought about by certain viral infections (e.g., by the papillomavirus).
What to watch out for
So how can you tell the difference between moles and skin cancer growths?
To know the difference, you first need to be observant. You need to know your dog’s natural personality and habits. You need to familiarize yourself with every mole and marking on your dog’s skin. So that if there are any changes in the markings’ color or size, you’ll catch them right away — and you’ll be able to alert your vet about such changes, ASAP.
Here are the specific changes you should watch out for:
- If your dog’s existing mole or moles have suddenly changed in size, shape, color, and firmness or texture (especially if the changes seem to be accelerated)
- If a new mole, weird skin growth, or skin discoloration suddenly appears elsewhere, seemingly overnight or in the span of a few weeks
- If your dog seems quiet, tired, lethargic, lacking in appetite, or having digestive/pooing problems (e.g., abnormally colored or bloody feces)
What to do
OK, let’s say you’ve found a mole on your dog that you suspect is cancerous. What should you do?
A major trip to the vet
Bring your dog to the vet immediately for a thorough check-up. Aside from making a thorough physical examination of your dog, your vet will likely schedule a blood test and a biopsy of your dog’s suspect “mole.”
The blood test is easy to perform. A bit of blood will be extracted via needle and syringe while your dog is awake. The biopsy, however, will require extraction of sample tissue — a minor surgery that involves anesthetizing your dog. Based on the outcome of those tests, the vet can then conclude whether the “mole” is malignant or not.
However, to keep your dog safe, a skilled and efficient veterinary surgeon will typically recommend immediate surgical removal of the entire suspected tumor, especially if it’s still small enough (instead of doing a biopsy, waiting for lab results, then performing a second surgery to remove the rest). He or she can then perform a lab analysis on the tissue that was taken out. If the analysis proves it’s malignant, at least your dog will already be safe.
Important Note: If the cancer has spread or if removal of the tumor is tricky, the vet might recommend radiotherapy or chemotherapy instead of surgery. The feasibility of these methods will depend on your dog’s age and overall health. If this ends up being the case with your dog, follow your vet’s advice on how to manage your dog’s health during treatment.
After surgery
Once the “mole” or tumor is removed, follow your vet’s advice on how to help your dog heal. You will likely need to put an e-collar around your dog’s neck to keep him from scratching or biting the surgical wound.
While your dog heals, give him the best dog food and the cleanest bed possible. And as always, keep a sharp eye on any strange growths or lumps that might pop up again on his body.
Final note
So don’t panic if you see a mole on your dog. With practice and careful observation, you’ll be able to tell the difference between a harmless mole and skin cancer!
