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Case Study: Moose and a Mast Cell Tumor

Sharon Shor, DVM, DACVIM (Oncology)
Moose, a 6-year-old French bulldog, presented to BluePearl in Tacoma last October for evaluation of a mass that grew rapidly, over a course of 2 weeks, on his muzzle. The mass was diagnosed by Moose’s primary veterinarian as an aggressive type of mast cell tumor (MCT) that caused severe swelling, redness and ulceration of the skin in the area. Typical to MCTs, the area was also itchy, and Moose constantly wanted to scratch the mass. Upon examination by our surgery service the mass was found to be too large to expect complete removal with surgery.

Moose was then referred to our oncology service. Because MCTs have a wide range of biological behaviors, it is important to recognize features that point to malignancy and a higher degree of aggressiveness. In Moose’s case, the size of the mass at presentation, its location on the mucocutaneous junction, its recent rapid growth and degree of swelling and skin ulceration were all markers for a tumor with a higher rate of malignancy.

During his initial evaluation, Moose had undergone staging tests to determine how far the tumor had progressed in his body, an important first step in evaluating dogs with more aggressive MCTs. Even if a mass appears amenable for surgery, the results of staging tests may change dramatically the overall prognosis for the patient and the decision made for how to treat the disease.

Moose was evaluated with blood and urine tests, cytological evaluation of the local draining lymph node and with imaging tests. An abdominal ultrasound was done in-house with our radiology service and found no abnormalities in the structure of organs. The spleen and liver were carefully inspected because they are known to be involved with some of the more malignant MCTs. Cytological evaluation with ultrasound-guided needle aspirates is sometimes used even if there are no structural changes in these organs; in Moose’s case, the spleen was evaluated cytologically and found to have no evidence of mast cell disease. Radiographs of his chest showed no evidence of other comorbid diseases (MCTs rarely spread to the lungs). Cytology of the mandibular lymph node found evidence of mast cells consistent with local spread (metastasis) of the disease.

At this point, I had a thorough discussion with the owner about the stage of Moose’s MCT and the options available for his treatment. Lymph node involvement was concerning, but the owner wanted to pursue any treatment that would address the local mass and give Moose the best chance to control the disease. Fortunately, past experience shows us that there are ways to reduce the size of these tumors before surgery with the end goal of getting them removed with complete surgical margins. A few drugs are available for treatment of MCTs including steroids, chemotherapy medications such as vinblastine and CCNU, as well as Palladia®. Moose was treated with a combination of CCNU, vinblastine and prednisone, and after a few short weeks of treatment, Palladia was prescribed in combination with vinblastine and prednisone. Combining conventional chemotherapy with Palladia is not without risk, and there is potential for bone marrow suppression and development of infections as well as other side effects. Special care is needed when deciding about the doses and frequency of treatments, and routine monitoring is necessary, ideally by a veterinary oncologist, to avoid complications for the pet with such an approach.

Moose responded amazingly well to the combination of chemotherapy and Palladia, and within a total of 5 weeks of therapy his mass reduced in size and flattened, and the skin healed to have no ulceration or redness. He was then able to undergo surgical removal of the local draining lymph node and the mass, which resulted in complete tumor excision. He healed from surgery well and is free from the irritation of the tumor that was on his nose. These days he continues treatment and routine evaluation with the Medical Oncology service in BluePearl Tacoma.

Moose is a success story, and we are very glad with his outcome. The initial evaluation process with medical oncology was very important and allowed appropriate setting of expectations with the owner. The collaboration between medical oncology and surgery was also crucial in providing this outcome.