Common Types of Cat and Dog Skin Cancer Malignant Tumors on a Pet

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Pets are at risk for a variety of skin cancers that must be caught and treated early.

Even the most conscientious pet parents who carefully plan nutritious diets  for their dog or cat and diligently visit the vet for annual checkups may not realize they need to take steps to protect their pet’s skin.

Skin cancer is the most common type of canine cancer and the second most common feline cancer. Not every lump or growth on a pet is a malignant tumor, but because certain types of skin cancer can be very aggressive and fatal, you should check your pet regularly for new bumps or changes in their skin. If you find anything unusual, take your pet to the veterinarian as soon as possible.
Here’s what you need to know about some common skin tumors.

Mast Cell Cancer

The skin tumors seen most frequently in dogs are mast cell tumors (MCTs). Among cats, MCTs are the second leading cause of skin cancer. Treatment and prognosis for your pet will depend on the grade of tumor, which can range from benign to highly malignant. Unlike the most prevalent forms of human skin cancer, sun exposure doesn’t seem to play an important role in mast cell cancer in pets since these tumors can develop on body parts heavily protected by fur or that don’t receive much sun.

In dogs, some breeds seem genetically predisposed to MCTs. Boxers, Pugs, Rhodesian Ridgebacks, and Boston Terriers are more likely than other breeds to develop mast cell tumors.

Cats can get the same type of MCTs as dogs but may also develop a rare form of mast cell cancer called histiocytic sarcoma. Siamese cats appear to be most at risk for both forms of feline MCTs.

What to look for: Skin MCTs often appear as single raised, hairless lumps. They’re usually white but may be pink. Canine MCTs often appear on the belly, back, sides, and limbs. Cats with MCTs usually have growths on their neck or head, including the ears.

Basal Cell Tumor

Basal cell tumors are often benign Even if your dog or cat develops the cancerous form, basal cell carcinoma, the tumor can often be successfully removed without further problems. Cancerous basal cell tumors are the most common skin cancer in cats. Middle-aged cats are most susceptible to these tumors along with Persians and other long-haired breeds. Many breeds of dogs are predisposed to basal cell tumors, including Wirehaired Pointing Griffons and Kerry Blue and Wheaten Terriers.

What to look for:  Basal tumors grow from deep within the skin’s layers. They may occur as a series of small nodular growths side by side on the back and chest of cats. On dogs, these tumors are more likely to appear as single hairless lumps on the head, neck, or shoulders.

Squamous Cell Carcinoma

Sun exposure plays a significant part in the development of squamous cell carcinoma, but other factors such as burn injuries or even viruses can also increase your pet’s risk. While other skin cancers are more common in dogs and cats, squamous cell carcinoma can be a more aggressive and deadly cancer if not treated early.

There are different types of squamous cell carcinomas, and different breeds of dogs are more susceptible to each type. Bloodhounds, Basset Hounds, and Standard Poodles are at greatest risk for one type, while white-skinned, shorthaired breeds such as Dalmatians, Bull Terriers, and Beagles are prone to another type. Older dogs are at the greatest risk. Cats with white skin and hair are more likely to develop squamous cell carcinoma because they are more vulnerable to UV radiation.

What to look for: Squamous cell carcinoma may appear as a white or grayish ulcer, cauliflower-shaped lump, or a red bumpy area. These growths may include sores that don’t heal. You may notice hair loss in the area (due to your pet constantly licking it). It’s common for these ulcers to appear on your pet’s belly since dogs and cats often sun themselves on their back. Pets are also at risk for oral squamous cell carcinomas, so you should check your pet’s mouth for ulcers as well.

Caring for Pets With Cancer

Several other skin tumors can affect dogs and cats in very different ways, including fibrosarcoma  melanoma, histiocytosis, and lipoma. Treatment for all types of skin cancer usually includes removal of the cancerous growth. Lymph nodes may also need to be removed, and radiation therapy or chemotherapy may be needed to treat inoperable tumors or to ensure that all the cancerous cells are eradicated. Paying attention to the special nutritional needs of pets with cancer is also an important part of helping your dog or cat heal.

The most important thing is to detect cancer early by regularly checking all areas and folds of skin for possible signs of skin cancer.

More on Cancer

Cancer in Dogs and Cats
Liver Cancer in Dogs and Cats
Hemangiosarcoma in Dogs and Cats


“Tumors of the Skin and Soft Tissues,” The Merck Veterinary Manual. July 2011 (accessed online November 22, 2013)

This information is for informational purposes only and is not meant as a substitute for the professional advice of, or diagnosis or treatment by, your veterinarian with respect to your pet. It has, however, been verified by a licensed veterinarian for accuracy.

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