Mast Cell Tumors in Dogs and Cats

Mast cell tumors occur in both dogs and cats. Although some are benign, most of these tumors are malignant.
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Mast cells are found in all tissues of the body, but they are in especially high numbers in the skin, respiratory tract, and gastrointestinal tract. Mast cells contain histamine and heparin. They play a role in allergic responses, non-allergic skin disease, wound healing and tissue remodeling. They can also increase stomach acid production.

When mast cells replicate in higher than normal numbers, a mast cell tumor can form. Pets with mast cell tumors can also have complications like stomach problems from the overproduction of histamine and excessive bleeding from the release of heparin.

Mast cell tumors occur in both dogs and cats. Although some are benign, most of these tumors are malignant. Mast cell tumors vary widely in their appearance, shape, and size. Dogs usually develop a single tumor. More cats than dogs develop multiple tumors.

If your pet has a mast cell tumor on the skin, there'll be a bump or lesion of some kind. Sometimes it's a raised pink bump on the surface of the skin. Sometimes it's a less-defined mass that feels like a lump under the skin.


Definitive diagnosis of a mast cell tumor is made through physical examination and testing, including tumor aspiration or biopsy.

If the fine needle aspirate reveals mast cells, the surgeon will take large margins around the tumor, which reduces the likelihood of leaving tumor cells behind. The tissue that is removed is sent to a pathologist for staging. This will let your vet know how extensive the disease is and what type of treatment is needed.

Mast Cell Tumors in Cats

In kitties, mast cell tumors are most often seen in the skin of the head or neck, but they can occur anywhere in the body. Cats with these tumors are usually middle age or older (4-plus years of age), but any cat can develop a mast cell tumor, including kittens. Siamese cats are at higher risk than other breeds and develop a specific type of tumor called a histiocytic mast cell tumor.

In the majority of feline cutaneous mast cell tumors, the treatment is removal of the entire tumor with surgery. Usually, one round of surgery removes the entire problem.

Frequently in cats, mast cell cutaneous lesions are benign. In some cases, surgery isn't even needed because the mast cells resolve on their own. Unfortunately, kitties with mast cell tumors on the inside of their bodies -- typically in the GI tract or the spleen -- carry a much poorer prognosis.

Canine Mast Cell Tumors

In dogs, mast cell tumors are most often found on the trunk, limbs, and in between the toes. The tumors occur more often in some breeds than others, including Boxers, Boston Terriers, English Bulldogs, Bull Terriers, Fox Terriers, Labs, Doxies, and Weimaraners. Prognosis for dogs depends on the tumor location, the extent of the tumor, the grade, and the type of treatment given.

Mast cell tumors of the skin are very different in dogs than cats. Surgery to remove the tumor is less invasive in cats, and the prognosis for a full recovery is much better in cats than in dogs.

Mast cell tumors with generally poor prognosis are those on the muscle, around the mouth or in internal organs, in the bloodstream or bone marrow, and ulcerated tumors. Mast cell tumors that cause GI ulceration or are large, fast-growing, or recurring also carry a much poorer prognosis.

Treatment of Mast Cell Tumors in Dogs

Historically, mast cell tumors have been graded on a scale of I to III in dogs, with grade III being the most serious and carrying the worst prognosis for recovery. Grade I mast cell tumors generally have an excellent curative rate as long as the whole thing is removed. Even with aggressive surgery, the recurrence rate for a grade II mast cell tumor is about 20 percent. The majority of dogs with grade III malignant mast cell tumors will experience spread of the tumor, and sadly, only a small percentage live longer than a year post-surgery.

Recently, a two-tier histologic rating system for canine cutaneous mast cell tumors has been proposed to more accurately predict biologic behavior. This rating system puts mast cell tumors into a low-grade or a high-grade category. Low grade tumors carry a good prognosis for full recovery; a high grade tumor carries a poor prognosis.

If Your Pet Has Been Diagnosed With a Mast Cell Tumor

If your pet has been diagnosed with a mast cell tumor, I recommend you work with an integrative or holistic vet to reduce the risk of recurrence. There are supplements that can naturally help reduce mast cell degranulation and reduce histamine release.

And I recommend you eliminate carbohydrates from your pet's diet and supplement with a rich source of omega-3 fatty acids such as krill oil.

And I absolutely recommend that you never again vaccinate a mast cell patient.

Dr. Karen Becker is a proactive and integrative wellness veterinarian. You can visit her site at:

Her goal is to help you create wellness in order to prevent illness in the lives of your pets. This proactive approach seeks to save you and your pet from unnecessary stress and suffering by identifying and removing health obstacles even before disease occurs. Unfortunately, most veterinarians in the United States are trained to be reactive. They wait for symptoms to occur, and often treat those symptoms without addressing the root cause.

By reading Dr. Becker's information, you'll learn how to make impactful, consistent lifestyle choices to improve your pet's quality of life.

For more by Dr. Karen Becker, click here.

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