clinical
Red Bank Veterinary Hospital is pleased to offer open enrollment in a clinical trial for the treatment of mast cell tumors.

Mast cell tumors are common skin tumors in dogs. They account for 20-30% of all skin tumors in dogs. They are a cancer of mast cells, which are cells important in the immune response, and often occur in dogs that have a history of allergic skin disease. About 50% occur along the trunk and perineum, 40% along the extremities and 10% along the head and neck. Mast cell tumors can occur as a solitary lesion or be multiple. They can be haired, ulcerated, pedunculated etc. and, because of their different appearances, are often called the great imitator. In most cases, dogs have a history of the mass being present and changing in size over time.

With mast cell tumors, several factors have been shown to be prognostic:

• Grade: Low grade tumors (Grade I) carry a better prognosis than high grade (Grade III).
• Clinical stage: Tumors spread throughout the body carry a worse prognosis.
• Location of tumor: Tumors along the perineum, perianal, and other mucocutaneous sites carry a worse prognosis.
• Systemic signs: Animals that are sick due to systemic disease don't do as well.
• Completeness of surgery to remove the tumor; Complete removal carries a more favorable prognosis.

Our recommendation for most tumors is as follows:
If the tumor is a Grade I or II and the surgery was complete (all cancer removed), dogs are monitored over time. With a complete surgery, up to 90-100% may never recur again. If surgery is incomplete, we recommend a second surgery. If this is not possible due to location, then we recommend radiation therapy (mast cell tumors are very responsive to radiation therapy and local control of 90% has been noted) for the tumor. Radiation involves 16 treatments on a Monday through Friday schedule and generally does an excellent job of local control. For cases that are incompletely excised and are not treated with radiation therapy, chemotherapy could be considered to prevent tumor recurrence. However, we generally use chemotherapy for higher grade tumors. More recent studies have shown there is a subset of Grade II tumors that behaves more aggressively. All Grade II tumors are evaluated with special stains to tease these ones out. This is called a mast cell tumor panel which evaluates a variety of markers associated with malignancy in mast cell tumors. If a more aggressive Grade II tumor is determined, these dogs are treated with chemotherapy.

If a Grade III is found and completely removed, we still recommend follow up chemotherapy because of the aggressive nature of this tumor. In case of incompletely excised Grade III tumors, we recommend either a second surgery or radiation therapy. A recent study found dogs with incompletely excised Grade III mast cell tumors had a median survival (50% alive) of 20 months. This is without any other therapy. It is our belief that with chemotherapy, these dogs would likely do even better.

Chemotherapy consists of vinblastine (IV) and Lomustine (orally) given at alternating cycles. Dogs are also placed on prednisone, which is a steroid that has anticancer effects against mast cell tumors. Concurrently, dogs are placed on gastrointestinal protection because this tumor often releases histamine into the blood, which can cause gastric ulcerations. The drugs we often use are Pepcid or Tagamet which block histamine's effect on the stomach.

• Wk1: CBC, Velban (IV)
• Wk2: CBC CCNU (oral)
• Wk3: CBC
• Wk4: Restart protocol for a total of 4-6 cycles.

In cases where the tumor cannot be removed due to size or location, we typically offer palliative radiation therapy and chemotherapy. This particular protocol involves 4 weekly doses of radiation followed by a 15 week course of chemotherapy. It is intended for patients that cannot be cured as it offers improvement in clinical signs and reduction in the size of the tumor. A recent abstract evaluated 65 dogs treated in this manner (some of which were treated at Red Bank Veterinary Hospital) and found that 42% of the tumors responded (completely or partially reduced in size) and an additional 30% had stabilization of their disease. Nearly half of these dogs had cancer spread and were treated after failing other traditional therapies which explains the relatively short duration of response (2 months) and overall survival time (3 months). Factors that significantly affected outcome were: grade of the tumor (Grade III did worse), location of the tumor (mucosal tumors experienced a remission duration of 5 months and an overall survival of 7 months), and if chemotherapy was continued after radiation therapy (survival of 3.5 months vs. 3 weeks if it was not). Although the survival time reported in this study is poor, palliative radiation therapy and chemotherapy can be offered for cases in which there is no other treatment option.

for more information
Contact the Red Bank Veterinary Hospital Oncology Service at (732) 747-3636.

• Craig A. Clifford DVM, MS, DACVIM (Oncology)-Trial Coordinator
• Rogers M. Fred III, DVM
• Siobhan Haney MS, VMD, DACVR (Radiation Oncology)
• Joshua L. Lachowicz DVM, DACVIM (Oncology)