5 Common Skin Cancers in Dogs — And How They’re Treated

Skin tumors are common in dogs. Dogs can get several types of skin cancer. Each layer and section of a dog’s skin can develop unique tumors, any of which could eventually turn cancerous.

The good news is that 60% to 80% of skin tumors in dogs aren't cancerous. But, it’s nearly impossible to tell if a tumor is cancerous by looking at it. So, it’s important to talk to your vet about any changes in your dog’s skin.

Skin cancer in dogs can look like:

• Changes to your dog’s skin or coat

• Unusual lumps, bumps, sores, or raised areas

• New pink, brown, black, red, or gray spots on your dog’s skin

If you notice these or any other skin changes, let your veterinarian know. Many skin growths can be easily removed with surgery when caught early. But it all depends on the type of skin cancer your dog has.

Below we will highlight the five most common types of canine skin cancer.

1. Mast cell tumor (MCT)

Mast cells are immune cells typically involved in allergic reactions. Mast cell tumors (MCTs) develop from normal white blood cells that turn cancerous. Mast cell tumors are the most common type of cancer diagnosed in dogs, making up about 20% of all canine skin tumors. MCTs are more common in older dogs, ages 8 to 10. 

Breeds at higher risk for developing MCTs are:

• Boxers

• Boston terriers

• Bulldogs

• Pugs

• Rhodesian Ridgebacks

• Golden retrievers

• Labrador retrievers

Signs and symptoms of mast cell tumors

Mast cell tumors are known as “great imitators” because they can have a wide range in appearance. Early-stage MCTs generally appear as raised bumps on the skin’s surface or lumps just under the skin. These tumors can change in size, even from one day to the next. They may also look like warts.

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MCTs can grow anywhere on your dog’s skin but are most frequently found on the limbs, chest, and lower abdomen. The release of histamine from tumors causes stomach ulcers in some dogs.

Other symptoms of mast cell tumors can include:

• Nodules or hives near the tumor site

• Enlarged lymph nodes

• Loss of appetite

• Stomach pain

• Welts

• Collapse

• Weight loss

• Bloody or black, tar-like feces

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Diagnosis and treatment for mast cell tumors

Surgical removal is recommended for all confirmed mast cell tumors. A veterinary pathologist will review a tumor sample and assign a grade to the tumor. The most common system used is a three-grade system.

Dogs with low-grade tumors have the best chance for a full recovery. High-grade tumors are more likely to spread to other tissues and organs, lessening the likelihood of a favorable outcome.

2. Malignant melanoma

A malignant melanoma develops from abnormal melanocytes, cells that create a skin pigment called melanin. These tumors grow quickly in dogs and often spread to other body areas, so an early diagnosis is critical. 

Cancerous melanomas occur less often in dogs than in humans. This type of cancer is more common in dogs with dark-colored skin. Breeds at greater risk for malignant melanoma include:

• Miniature schnauzers

• Standard schnauzers

• Scottish terriers

Signs and symptoms of malignant melanoma

Malignant melanoma is often found on a dog’s skin, mouth, toes, or the nail bed. Melanoma usually appears as brown or black raised lumps on the skin but can look like gray or pink lumps in the mouth.

Malignant melanomas around the nail bed generally show up as swollen toes. The dog can even lose the toenail and have damage to the underlying bone. Limping may be the first sign you spot that your pup has an issue with their nail bed. Your dog may also lick or chew the affected toe.

Diagnosis and treatment for malignant melanoma

Once a dog is diagnosed with malignant melanoma, staging is highly recommended. This will help you find out if their cancer has spread to other areas.

Because this type of tumor can spread to lymph nodes and lungs, treatment with chemotherapy or immunotherapy is recommended following surgery.

3. Squamous cell carcinoma

Squamous cell carcinoma (SCC) is a rare form of skin cancer in dogs. An SCC is a cancerous tumor that starts in the skin cells. It’s often caused by exposure to sunlight.

SCC tumors are usually found on light-skinned, hairless, or thinly haired areas of a dog’s body. Short-haired dogs who spend significant time outside also have a higher chance of developing squamous cell carcinoma. Large-breed, dark-haired dogs are more prone to SCC of the digits (toes).

Certain dogs are more at risk for developing this cancer than others. Breeds at higher risk include:

• Bloodhounds

• Collies

• Beagles

• Bull terriers

• Scottish terriers

• Pekingese

• Boxers

• Poodles

• Norwegian elkhounds

Signs and symptoms of squamous cell carcinoma

This cancer generally appears as one tumor in a single location on the body. Tumors can grow outward into large masses that look like warts on the surface. They can turn red and become open sores, particularly on the toes.

It can be challenging to tell if these are tumors or warts. But open sores on the feet can become infected and painful.

Diagnosis and treatment for squamous cell carcinoma

SCC is typically diagnosed using a fine needle aspiration, which removes cells from a tumor. Sometimes, a biopsy may be needed to confirm the diagnosis. 

Treatment involves surgery to remove the primary tumor. Any remaining part of the tumor is usually treated with radiation therapy to prevent it from regrowing. Research suggests dogs with the skin version of squamous cell carcinoma can live more than 2.5 years after diagnosis.

Although squamous cell carcinomas rarely spread to surrounding lymph nodes, they can grow and metastasize. Squamous cell carcinoma can also form in a dog’s mouth. Though not skin cancer, squamous cell carcinoma is a common type of oral cancer.

4. Histiocytic sarcoma

Histiocytic sarcoma is an aggressive form of cancer, usually seen in middle-aged and older dogs. But dogs of any age can get it.

While any dog breed can develop this tumor, the most commonly affected breeds are:

• Bernese Mountain dogs

• Flat-coated retrievers

• Golden retrievers

• Labrador retrievers

• Rottweilers

Signs and symptoms of histiocytic sarcoma

Histiocytic cancer tumors can sometimes cause a visible mass on your dog, but not always. They can also cause symptoms you may see with other cancers or illnesses, such as:

• Fever

• Weight loss

• Loss of appetite

• Lethargy

Diagnosis and treatment for histiocytic sarcoma

If your dog is diagnosed with a histiocytic skin tumor, your veterinarian will want to do a complete workup to see if the cancer has spread to other body parts.

A complete diagnostic workup includes:

• Blood tests

• Urine sample

• Serum chemistry profile

• Lymph node biopsy

• Chest X-rays

• Abdominal ultrasound

The tests will reveal how the cancer is affecting your dog’s body. Tests will also help your veterinarian find the best treatment plan for your dog.

If the tumor is on a dog’s skin or in the bones, surgery is typically performed to remove it. But chemotherapy may be recommended if the cancer spreads to your dog’s other organs.

5. Fibrosarcoma

A fibrosarcoma is a soft-tissue tumor that develops in the connective tissue just under the skin. These tumors usually appear on a dog’s limbs and trunk. But they can also occur in the mouth and nose. In rare cases, fibrosarcomas can start in the jaw or leg bones.

Fibrosarcoma typically affects middle-aged to older dogs. Breeds with a higher risk of developing fibrosarcoma include:

• Gordon setters

• Irish wolfhounds

• Brittany spaniels

• Golden retrievers

• Doberman pinschers

Fibrosarcomas are slow-growing, and they rarely spread to other parts of the body. But they can invade the surrounding tissue and muscles.

Signs and symptoms of fibrosarcoma

Fibrosarcomas in dogs differ in size and appearance. Tumors located directly beneath the skin may appear as firm, solid lumps. If there is more than one tumor, they are usually in the same location.

Fibrosarcomas located in the soft tissue are often not visible. You may notice swelling in the affected area or signs that your dog is in pain.

If your pup is in pain, they may:

• Withdraw from social interaction

• Have less interest in food

• Refuse to be touched

If the tumor is in your dog’s mouth or nose, you may notice any of the following signs:

• Mucus discharge from the nose or eyes

• Excessive tearing

• Bleeding from the nose

• Sneezing

• Snoring

• Pawing at their muzzle

• Difficulty picking up food

• Trouble eating or swallowing

• Excessive drooling

Diagnosis and treatment for fibrosarcomas

A biopsy is the preferred method to diagnose fibrosarcomas in dogs. Your vet may order X-rays or a CT scan if they think your dog’s tumor might involve a bone. Surgical removal of the tumor is the first treatment choice, although many tumors come back within a year following surgery.

How is dog skin cancer diagnosed?

To help diagnose skin cancer, your vet will look at cells from your dog’s tumor under a microscope. There are two procedures to get samples of the cells:

Fine needle aspiration

During fine needle aspiration, a small needle is placed into the mass on your dog. Then a syringe is used to draw out some cells. This method is used to diagnose most mast cell cancers.

Biopsy 

To perform a biopsy, a veterinarian makes a small surgical cut in the tumor to remove a tissue sample. Or your vet may remove the entire tumor during surgery and find out if it’s cancer afterward. This is also a biopsy.

Analysis

The collected cells or tissue samples are placed on a slide and sent for analysis by a board-certified veterinary pathologist. They will look for cancerous cells in your dog’s sample to make a diagnosis.

Depending on the type of cancer your dog has, your vet may order other lab tests.

How do you treat dog skin cancer?

Treatment for a particular tumor depends mainly on the:

• Type of tumor/skin cancer

• Tumor location and size

• Your dog's overall health

• The cancer’s stage and whether it has spread

Many skin tumors are removed through surgery. Surgery is often the most effective and least costly treatment with the fewest side effects. Sometimes, your vet will remove your dog’s tumor and any lymph nodes affected by the cancerous cells.

Some tumors may need extra treatment with chemotherapy and radiation following surgery.

How serious is dog skin cancer?

Cancer in your dog is always something to take seriously. But the outlook for a dog with skin cancer depends on several factors. These include the type of skin cancer and how early the diagnosis is made. Your veterinarian can give you a better idea of what to expect for your dog.

Several types of skin cancer can affect dogs. The good news is that many can be successfully treated with surgery alone. Spotting signs of skin cancer in its early stages is critical to successful treatment outcomes.

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Written by:

Lauren Lee, BA, MA

Lauren Lee, BA, MA, is a writer specializing in animal care and pet health content. Since she was a young child, her passions have been writing and anything to do with animals.

Edited by:

Renée Fabian, MA

Renée Fabian is the senior pet health editor at GoodRx. She’s worked for nearly 10 years as a journalist and editor across a wide range of health and well-being topics.

Reviewed by:

Ghanasyam Bey, DVM

Ghanasyam Bey, DVM, is from Cleveland, Ohio, and attended Princeton University for undergraduate studies. After a year of biology research at Duke University, he attended Ohio State College of Veterinary Medicine.

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