Mast Cell Tumors in Dogs – Signs, Diagnosis, Treatment, and Prognosis

Mast cell tumor

By Kathy Otero, DVM and Dale Kaplan-Stein, DVM

A mast cell is part of the body’s immune system and plays an important role in mediating inflammatory responses. Mast cells are found in the skin, respiratory system, and intestinal tract and contain inflammatory biochemicals such as histamine. Mast cell tumors are growths that most commonly affect the skin, but may also infiltrate the spleen and liver.

There are many different types of skin tumors that can occur. In both dogs and cats, about 20% of skin tumors are mast cell tumors. Unfortunately, 50% of mast cell tumors in cats present in the spleen. Middle-aged and older pets present more commonly with this type of tumor. Boxers, English Bulldogs, Boston Terriers, Sharpeis, Golden retrievers, Schnauzers and Labradors, along with Siamese cats, are at a higher risk of developing mast cell tumors when compared to other breeds.

Mast cell tumors of the skin are first noticed as a small mass that does not change, until it suddenly enlarges.  As mast cell tumors grow the probability of the tumor spreading to internal organs increases. Because of the nature of this tumor, laboratory testing (complete blood count, biochemistry profile, and urinalysis) and diagnostic imaging (radiographs and ultrasound) are important tests to screen the body for tumor involvement. Boxer Mast Cell TumorDiagnosis can often be made with a fine needle aspirate, which is a non-invasive and painless procedure, performed without anesthesia. A small needle is inserted into the mass and cells are aspirated and then placed on a slide and studied under the microscope. Prior to handling mast cell tumors, pets are pretreated with anti-histamines to prevent potentially dangerous effects of sudden histamine release. This can cause tissue swelling and a serious drop in the pet’s blood pressure.

There are three components in the treatment of mast cell tumors. Surgical removal is the mainstay for any treatment, followed by radiation therapy and chemotherapy. These treatment options may be used alone or in combination depending on the grade of the tumor. Your veterinarian will discuss the best treatment plan for your pet. When surgery is performed, the tumor will be removed with wide margins, meaning a large portion of the surrounding tissue will be removed along with tumor in order to include all of the involved tissues and hopefully  prevent regrowth. After surgical removal and further examination by a veterinary pathologist the growth will be graded and determined if the removal is considered curative. Further testing and treatment might be necessary. The prognosis is variable and depends on many factors.

Early detection of serious disease can be life-saving. Therefore, semi-annual physical exams by your veterinarian is strongly recommended. Owners should be alert for any new skin masses and have them checked promptly. Some pets can develop more than one mast cell tumor, so a thorough physical exam is necessary. Mast cell tumors that involve internal organs may cause vomiting, decreased appetite, and/or lethargy.

Dr. Kathy Otero graduated in 2012 from Ross University School of Veterinary Medicine. After graduating she studied acupuncture at the world-famous Chi Institute in Reddick, FL. Her veterinary interests include internal medicine, dermatology, and acupuncture. Dr. Otero is a Gainesville, FL Veterinarian and practices at Oaks Veterinary Hospital. Dr. Dale Kaplan-Stein, a 1981 graduate of the UF College of Veterinary Medicine, has been at the forefront of progress in companion animal practice. She established Oaks Veterinary Hospital in 1982, and Northwood Oaks in 1995.