Mast Cell Tumors in Dogs

Mast cell tumors in dogs are one of the most common types of tumors. While they can be either benign or malignant, mast cell tumors can be extremely dangerous to the health of dogs.

Mast cells are a type of cell that is found in the skin and other tissues of the body, including the intestine. They are a part of the immune system and contain proteolytic enzymes, heparin and histamines. Mast cells help to repair tissue in the body by releasing inflammatory mediators.

Symptoms of a Mast Cell Tumor in a Dog

Mast cell tumors in dogs vary a great deal in their appearance. Most mast cell tumors in dogs often look like insignificant spots on the skin. Some mast cell tumors in dogs are above the skin, while some can be below. Mast cell tumors in dogs can be a variety of colors, while most are black or red. The tumors can appear with a variety of different textures, including bumpy, smooth and ulcerated. While the mast cell tumors in dogs can appear anywhere, they typically tend to show up on the arms, trunk and genital areas.

Diagnosis of a Canine Mast Cell Tumor

The most non-invasive way in which to determine if your dog has a mast cell tumor is to perform a fine needle aspirate. In this procedure, a needle is entered into the tumor in an attempt to extract cells. The doctor or laboratory looks at the cells under a microscope to see if the tumor is indeed a mast cell tumor. The dog usually does not have to be sedated for this as this procedure usually inflicts the same amount of pain as a blood draw.

A biopsy is usually the most definitive way in which to diagnose if your dog has a mast cell tumor, but this requires surgery and anesthesia. If the veterinarian suspects that the mass is a mast cell tumor, he will generally take wide margins when removing the lump. The sample is then sent off to a laboratory where a pathologist biopsies the tumor.

Treatment for Mast Cell Tumors in Dogs

Treatment of mast cell tumors in dogs depends upon the severity and grade of the tumors. There are three grades in which a mass cell tumor can be. A grade one tumor is benign and tends to not spread in the body. Grade two spreads into the subcutaneous tissue and can often be malignant. Grade three is very aggressive and is found in deep tissue. There are five different stages in determining the severity of mast cell tumors with stage zero as the least dangerous and stage four the worst.

If the mast cell tumor is a grade one or two, surgical excision usually cures the problem. Radiation is recommended when the mast cell tumor can not be removed or when the margin around the tumor cannot be made wide enough. Chemotherapy is generally used on aggressive mast cell tumors in combination with anti-cancer drugs.


The prognosis for a dog with a mast cell tumor depends upon the severity of the grades and stages. Typically, a dog who has a low stage and grade mast cell tumor does better than a dog with a higher stage and grade. However, the sooner the tumor is removed and treated, the better the chances a dog has for recovery.