How do you tell if a dog s mole is cancerous

6 Types of Moles on Dogs [With Pics] and What to Do

This article was updated on October 16th, 2023

When an owner comes to my clinic because they are worried about a new growth or mole on their dog, the question on everyones lips is, What is it?.

When a new skin lesion resembles a mole, owners will inevitably wonder: do dogs have moles? The answer is yes. However, we refer to them as nevus (singular) or nevi (plural). Some owners and vets, however, will use the word mole interchangeably with skin tag or wart.

Types of moles (with pictures)

Technically, a mole is a nevus. This is a benign skin growth that is usually small and quite symmetrical. Uncommonly, a nevus can be cancerous or can transform into a cancer. Cancerous moles on dogs are quite rare, thankfully.

As mentioned, other types of lesions such as a cyst, skin tag or wart may also be referred to as moles by some people. Lets take a look at some of the more common types of moles or bumps in dogs, with pictures:

Skin Tags

In older dogs especially, skin tags start to appear. We often see them on the face, elbows, armpits, and ankles. They can dangle from the skin and may be dark or a fleshy pink color. They are slow-growing and should not bother the dog.

Generally, we would monitor skin tags but would not remove them unless they were becoming a nuisance. Learn more about Skin Tags.

Cysts

Dogs develop all kinds of cysts, some of which are fluid-filled and others that contain a thicker substance that resembles cottage cheese.

Canine cysts can appear anywhere on the body and may grow to a substantial size. However, most cysts remain quite small. If a cyst is drained or ruptures, it will refill quickly. While cysts usually do not need to be removed, removing one involves a surgical procedure to extract the cyst wall. Learn more about Cysts in Dogs.

Warts or sebaceous adenomas

Warts tend to be light pink and can resemble small cauliflowers or brains. We tend to see warts in two dog populations: puppies and seniors. This is because both of these age groups struggle to fight off infections and warts are spread by a virus. For younger dogs, warts usually resolve within a few months. For older dogs, they may persist and grow slowly over time. Learn more about Warts in Dogs with pictures and veterinarian info.

Cancer

Cancerous lumps come in all shapes and sizes, as shown in the pictures below.

A black mole on a dog (rather than white, pink or red) is more likely to be a cancer called melanoma. Some of the more common places where malignant melanoma occurs include the mouth, near the claws, and sometimes within the eye. Learn more about Cancerous Lumps.

True nevi

A small black or brown mole on a dog may be a true nevus. These moles can appear on the face, flank, and paws, as well as other locations. As these lesions are benign, there is generally no need to intervene or provide treatment. However, a vet may discuss sampling the lesion to rule out anything more sinister, such as a melanoma.

Related post: Pictures of Common Lumps & Bumps on Dogs.

What to do when you find a mole or bump on your dog

1. Take pictures: When a new bump is noticed, it is a good idea to snap a photo, so you can assess if it is growing or changing over the coming days and weeks.

2. Consider a buster collar: If your dog has been licking or chewing at it, it is wise to use a buster collar to prevent this. This helps ensure the lesion does not become infected.

3. Reach out to your vet: A lesion that is not going away after a few days should be examined by a vet. Most of the time, new moles or warts will be something we monitor. Less often, your vet may discuss sampling or removal of the lump, particularly if they are concerned about cancerous tumors such as melanomas or mast cell tumors.

When is it ok to wait-&-see?

If youve only just noticed a small lesion and it is not bothering your dog, you may monitor it over a few days. It could be a small scab or insect sting, which will resolve quickly.

It is sensible to consult your veterinarian if the new lesion is persisting for over a week or if it seems to be quickly growing and changing. A consultation should also be booked if a lesion suddenly gets bigger or becomes infected.

Veterinary treatment, costs, and recovery

For many new lumps and bumps, the cost involved may be limited to the consult (about $60-100), as the vet may feel that the lesion is likely benign and needs no intervention. However, it is important to remember that the only way to know this is to sample and test the lesion.

If the mole needs to be investigated, this will be more costly. This can involve a Fine Needle Aspirate ($150-250) or biopsy ($200-400).

Removing a mole may be more costly, as it usually means the pet needs to be under an anesthetic. This can mean a bill of $400-900. This price should include the lab fees for analyzing the growth.

Frequently Asked Questions

What causes the growth of moles or bumps in dogs?

There is likely a large genetic component when it comes to the development of these lesions, but other factors can play a role, too.

• Exposure to sun. Dogs who spend a lot of time in the sun, particularly those who are short-furred, seem more prone to moles and skin tags.
• Weight gain. Dogs who carry more fat than they should can be more prone to developing certain lesions.
• Friction. When skin rubs against itself, especially in places like the armpits and groin, this can lead to skin tags developing.

Can moles or bumps on dogs be cancerous?

Yes, it is possible for these skin lesions to be malignant, which is why a vet visit should be booked for any lesion that is not going away quickly. Read our article about cancerous lesions and bumps in dogs.

How can I differentiate between a benign and malignant mole or bump?

There is no definitive way to do this without sampling the lesion and looking at it under the microscope. However, malignant lesions do share certain characteristics, such as being quick to grow, ulcerating, and becoming infected. Learn more: cancerous lesions and bumps.

Can moles or bumps on one dog spread to other dogs or humans?

No, moles cannot spread and are not contagious. Warts (papillomas), on the other hand, can spread from dog to dog.

Are certain dog breeds more prone to developing bumps?

Yes, there is a genetic component, so we will see certain lumps more often in certain breeds. Poodles, Schnauzers, and Golden Retrievers may be over-represented.

• Dr Linda Simon (MVB MRCVS) has 10 years of experience as a veterinarian. She is a veterinary surgeon with a special interest in geriatric patient care, dermatology and endocrinology. She is a member of the British Royal College of Veterinary Surgeons. She graduated top of her class from UCD School of Veterinary Medicine in Dublin in 2013. Linda has also worked as a locum vet in a range of clinics, including 24 hour emergency clinics and busy charity clinics.

  View all posts

Disclaimer: This website's content is not a substitute for veterinary care. Always consult with your veterinarian for healthcare decisions. Read More.

Dog Skin Cancer: Types, Symptoms, and Treatment

The word cancer instills fear into the heart of every dog owner, but not all growths are cancerous. The most common growth found on dogs are lipomas, which are fat cells. Also commonly found on dogs are sebaceous cysts, which can become cancerous. If your veterinarian has diagnosed your dog with skin cancer, or if you are concerned that your dog might have a cancerous skin tumor or lump, it is understandable to feel worried and fearful.

Your veterinarian is your best resource to help you through any questions you may have about your dogs health and skin issues. However, here is some information you need to know about skin cancer in dogs to help you understand your dogs possible condition.

Can Dogs Get Skin Cancer?

Dogs can get skin cancer, just like we can. In fact, skin tumors are the most commonly diagnosed type of tumor in dogs. This is partly because skin tumors are easier to see with the naked eye than other types of tumors, and partly because the skin is exposed to more of the environmental factors that can cause tumors, such as chemicals, viruses, and solar radiation, then your dogs internal structures. Luckily, this also means that you and your veterinarian have a better chance of catching your dogs cancer before it progresses past available treatment options.

Causes of Skin Cancer in Dogs

Skin cancer can have a variety of causes. Just like with people, genetics play a large role in which dogs are more likely to get skin cancer. In fact, it is believed that genetics are the number one factor in the risk of a dog getting skin cancer. Triggers that may lead to a dog developing skin cancer include too much exposure to the sun, chemicals in the environment, hormonal abnormalities, and certain types of viruses.

Types of Skin Cancer in Dogs

There are several different types of skin cancer in dogs, just like there are several different layers of the skin. Each layer and skin component can develop distinct tumors, some of which may turn out to be cancerous.

Some of the more common types of skin cancer in dogs are:

• Malignant melanoma
• Mast cell tumors
• Squamous cell carcinoma
• Histiocytic cell tumors
• Fibrosarcoma

Malignant Melanoma

Melanomas can be either malignant or benign. These tumors are often dark-pigmented or can lack pigment. While benign melanomas are more common, malignant melanomas are a serious concern, as they grow quickly and have a high risk of metastasis (spreading to other organs).

Malignant melanomas are most commonly found on the lips, mouth, and nail beds. According to some researchers, the head, neck and scrotum areas are also moderately predisposed to skin cancer. Certain breeds, for example Miniature and Standard Schnauzers and Scottish Terriers, are at an increased risk, and males appear to be affected more than females.

Malignant melanomas look like raised lumps, often ulcerated, and can also look like gray or pink lumps in the mouth. Nail bed malignant melanomas, on the other hand, show up as toe swelling and possibly even loss of the toenail itself and destruction of underlying bone. Nail bed and footbed tumors often develop a secondary infection, leading to a misdiagnosis. These types of tumors usually metastasize to other parts of the body, decreasing the chances for a good outcome.

Mast Cell Tumors

Mast cell tumors are the most common types of skin cancer tumors. Mast cells release histamine, which is the chemical that causes some of the symptoms of allergic reactions in dogs, like irritation and itching. Mast cell tumors are cancer of these cells, and they can grow anywhere on your dogs skin, as well as in internal organs. The most common sites for mast cell tumors are the limbs, lower abdomen, and chest. About of mast cell tumors are found on dogs limbs.

Boxers, Pugs, Rhodesian Ridgebacks, Boston Terriers and older mixed breed dogs seem particularly susceptible to mast cell tumors, which most commonly affect dogs ages 8-to-10 years old. This cancer can be difficult to deal with, and your dog could have symptoms associated with toxins released from malignant mast cells, such as stomach ulcers, resulting from histamine release.

Squamous Cell Carcinoma

Skin squamous cell carcinoma is the most commonly diagnosed carcinoma of the skin, and primarily affects older dogs, especially Bloodhounds, Basset Hounds, and Standard Poodles. These tumors typically show up on the head, lower legs, rear, and abdomen, and appear as raised patches or lumps that are firm to the touch.

Exposure to the sun can be a cause of squamous cell carcinoma, but according to the National Canine Cancer Foundation, In dogs, the theory of exposure to sun is less obvious. It is believed that there may be some association with papilloma virus.

These tumors usually appear on your dogs abdomen, which is the area least protected from the sun by hair.

Histiocytic Cell Tumors

Histiocytic cells are a type of skin cell. When these cells proliferate into tumors, they are classified as histiocytic cell tumors.

These types of tumors are relatively common and typically affect dogs under 3 years old, especially Scottish Terriers, Bulldogs, Greyhounds, Boxers, Boston Terriers, and Chinese Shar-Pei.

There are three types of histiocytic cell tumors: histiocytomas, which are the most common; systemic histiocytosis, which mainly affects Bernese Mountain Dogs; and malignant histiocytosis, which also mainly affects Bernese Mountain Dogs and first shows up in the internal organs.

Fibrosarcoma

Fibrosarcoma and spindle cell tumors originate in the connective tissues of the skin and beneath the skin. These tumors can have a varied appearance, and while they are typically slow growing, they do tend to recur after surgical removal. Luckily, this type of tumor rarely metastasizes.

Fibrosarcoma usually affects dogs when they are middle-aged or older, with an average age of 10 years. Sometimes, an aggressive type of fibrosarcoma can affect young dogs. Your veterinarian will send off a sample of the tumor to a pathologist to determine whether or not the tumor is a low- or high-grade tumor, a classification that refers to the rate of cell division. This will help them give your dog an accurate prognosis and determine the best course of treatment.

This type of tumor is often found on the limbs. In addition to invading nearby structures, sometimes impeding their function, the tumors can also bleed, ulcerate, and become infected.

Symptoms of Skin Cancer in Dogs

The symptoms of skin cancer vary depending on the cancer, but in general, the best thing you can do to catch skin cancer early is to keep an eye on any strange lumps or bumps on your dogs body, especially as he ages.

Not all skin tumors are cancerous, and some, like skin tags, are usually benign sebaceous cysts or lipomas. However, if you discover an unusual lump or area of discoloration, play it safe and contact your veterinarian. Changes in the size, shape, color or ulceration of any growth or lump are also a cause for concern.

Diagnosing Skin Cancer in Dogs

Dog skin cancer is diagnosed by examining the cells of the skin tumor or lesion. Your veterinarian may perform a procedure called a fine needle aspiration, which takes a small sample of cells, or a biopsy, which removes a small portion of the tumor tissue or lesion by surgical incision. These samples are usually sent away to pathology for evaluation in order to obtain an accurate diagnosis.

Skin Cancer Treatment Options

A diagnosis of cancer for your dog is scary. Many types of skin cancer are treatable if caught early on, but it is understandable to feel worried.

Your dogs prognosis and treatment options will depend on a few factors, including the type of tumor, the location of the tumor, and the stage of the cancer.

Some skin tumors can be removed surgically to great effect. Others may require additional steps, such as radiation or chemotherapy.

Some types of cancer, for example malignant melanomas, are resistant to radiation therapy, while others, such as mast cell tumors, are more sensitive. Your veterinarian may refer you to a veterinarian oncologist when you have a cancer diagnosis. Veterinary oncologists have advanced training in cancer treatment.

Preventing Skin Cancer in Dogs

Some types of diseases are preventable, while others are not. As in humans, many cancers are the result of a genetic predisposition. In other cases, cancer is the result of a variety of factors coming together in an unlucky configuration, but there are a few things you can do to lower your dogs risk.

The risk factor most in your control is exposure to sunlight. If you have a light-skinned, short-haired dog breed, limiting your dogs exposure to direct sunlight, especially during the peak daylight hours, may help lower his risk of skin cancer.

The most important thing you can do to help your dog avoid skin cancer, however, is to familiarize yourself with all your dogs lumps, bumps, and rashes, perhaps during your daily grooming routine, and consult your veterinarian if you notice anything suspicious.