Mast Cell Tumors

Mast Cell Tumors:

Mast cell tumors are the most common type of skin tumor found in dogs and the second most common skin tumor in cats. These represent 14–21% of all skin tumors diagnosed in dogs. They are usually noticed in middle aged patients, but can occur in patients of any age. Boxers and Boston terriers make up ~ 50% of all cases. Other common breeds affected include:

  • Pugs
  • Bullmastiffs
  • Cocker spaniels
  • Bull terriers
  • Staffordshire terriers
  • Fox terriers
  • Labrador retrievers
  • Golden retrievers
  • Beagles
  • Schnauzers
  • Weimaraners

Most tumors are solitary although boxers and pugs have an increased predilection for multiple skin tumors. These tumors most often are noticed in the skin and subcutaneous tissue. Common locations in the dog include:

  • Trunk  42–65%
  • Limbs  2–43%
  • Head and neck 10–14%

Visceral (intra-abdominal organs) mast cell disease is a recognized form of the disease and is more aggressive than the aforementioned locations. This is often preceded by skin or subcutaneous tumors.

Signs and Symptoms: 

Your pet’s clinical signs will relate to the grade and progression of the disease. Some pets will be presented with small, freely movable tumors in the skin or subcutaneous tissues with minimal surrounding inflammation. Other pets will be presented with large, ulcerated, and hairless tumors often associated with a more aggressive tumor. Clinical signs such as vomiting, loss of appetite, and digested blood present in the stool are also possible. The grade and subsequent prognosis related to the tumor cannot be determined until it is removed and submitted to histopathology for analysisanalysis biopsy and histopathologic analysis has been performed.

Mast cell tumors can vary in size from day to day depending on the degree of inflammation secondary to the degranulation of the cells. These granules contain histamine, proteolytic enzymes (denature proteins), and vasodilatory substances responsible for the redness and swelling surrounding your pet’s tumor. These same factors can also effect the gastrointestinal tract causing ulcers resulting in clinical signs such as vomiting, lack of appetite, melena (bloody stool), anemia (low red blood cells), and abdominal pain.


Surgical removal of mast cell tumors is the preferred treatment once your pet is diagnosed with this disease. Mast cell tumors invade into surrounding tissues and wide surgical margins (wide area of healthy tissue surrounding the tumor) are necessary to ensure removal of all cancerous cells. The excised (removed) tumor will be submitted for histopathology for confirmation of the tumor type and grading.

Post-surgical radiation and chemotherapy are warranted on a case-by-case basis. Radiation is most commonly used as a multi-modal treatment approach for incompletely excised tumors. Chemotherapy is used in patients with disseminated disease to other organs or high grade tumors. The surgeons at CVSS work cosely with your pet’s primary care veterinarian to make the most appropriate recommendation for your pet’s continued care following surgery.

Articles and Photos Courtesy of the American College of Veterinary Surgeons