Medical Oncology: Canine Multiple Cutaneous Mast Cell Tumors

• Canine Multiple Cutaneous Mast Cell Tumors (downloadable PDF flyer)

What Are Multiple Cutaneous Mast Cell Tumors?

Mast cells contain chemicals that are involved in allergic reactions. When dogs develop tumors of these cells in their skin, they are called cutaneous mast cell tumors. Some dogs develop only one mast cell tumor during their life. Some develop many tumors over months or years. Others develop several tumors simultaneously. When this happens, the dog is diagnosed with “multiple cutaneous mast cell tumors.”

Most dogs with multiple cutaneous mast cell tumors present with small tumors that grow slowly. These are usually low-grade tumors, meaning they are not likely to bother the patient or spread and cause illness. It is possible to monitor such patients over time. Affected dogs are likely to continue forming new tumors.

Some dogs with multiple cutaneous mast cell tumors have an aggressive form of the disease. Tumors grow rapidly and can spread to lymph nodes, internal organs, and other body areas. The prognosis for those dogs is usually poor.

What Diagnostics Are Performed?

A small needle is inserted into the tumor, and cells are removed. The cells are examined under a microscope. Some dogs need surgery to confirm the diagnosis. All lumps/bumps should be checked to ensure the diagnosis and provide a baseline for future monitoring.

Further testing (staging) is recommended. This includes blood and urine tests, lymph node sampling, and abdominal ultrasound (+/- sampling of the liver and spleen). Bone marrow testing is done in some dogs. Thoracic radiographs (x-rays) can be done, but the lungs are not a common site for spread. These tests also provide a baseline for future monitoring. They provide information about the patient’s overall health. Results may influence treatment recommendations. They can also help anticipate complications. Staging can help predict prognosis.

What Are The Treatment Options?

Surgery is recommended for most mast cell tumors. This is true for dogs presenting with one tumor, dogs who develop more than one mast cell tumor over time, and dogs with multiple cutaneous mast cell tumors. After removal, further treatment depends on the grade(s) of the tumors and margins.

Surgery may not be an option for all dogs with multiple cutaneous mast cell tumors. The dog may not be a good candidate for anesthesia, the tumors may not be able to be removed entirely, there may be too many tumors to remove safely, or an owner may not wish to pursue it. In such cases, we can try non-surgical options to control the disease.

Stelfonta® (tigilinol tiglate) is a non-surgical /non-chemotherapy option for mast cell tumors. It is a drug that is injected directly into the tumor. The drug causes the tumor cells to die, leaving behind a wound left open to heal over time. Tumors must meet specific criteria for size and location for this treatment. The chance of a tumor responding to treatment is 75% with one injection and 87% with two injections. 90% of dogs treated with Stelfonta were tumor-free one year after treatment. A downside to treatment with Stelfonta is that the grade of the tumor cannot be determined, and therefore risk for spread and aggressive behavior cannot be assessed.

Additionally, it is not recommended to treat more than one tumor at a time, and there is a maximum amount of this drug that can be injected. Therefore, it is not often a realistic option for dogs with multiple cutaneous mast cell tumors. The approximate cost per injection is $500.

Chemotherapy drugs used to treat mast cell tumors in dogs are shown in the table below.

Drug	How is it given?	How often is it given?	Chance of response	Approximate Cost *
Vinblastine	Intravenously	Every 1-2 weeks	40-50%	$300-$400 per treatment
CCNU	Orally (in hospital)	Every 3 weeks	40-50%	$300-$400 per treatment
Palladia®	Orally (at home)	Every other day	45%	Varies greatly with body weight

Responses for any of the drugs listed above last about 3-4 months before tumors grow or new tumors form. Therefore, most dogs with multiple mast cell tumors treated with chemotherapy receive all three drugs over time. This is typically not curative.

Another non-surgical option is treatment with prednisone (oral steroid) alone. Though published data suggests a high response rate (70%), this overestimates our clinical experience of expected response with prednisone alone. We often combine prednisone and the chemotherapy drugs listed above to try and increase the chance of a response.

One of the most common questions we are asked is if there are any chemotherapy drugs or other treatments that will stop dogs from developing new tumors.

Unfortunately, no medical therapies will prevent dogs with multiple cutaneous mast cell tumors from developing new mast cell tumors.

While understandably frustrating for pet owners, the good news is that many dogs with multiple low-grade tumors can have an expected lifespan.

Medications reduce the chance of an allergic reaction in the entire body. This includes antihistamines (diphenhydramine/Benadryl®) and antacids (famotidine/Pepcid® or omeprazole/ Prilosec®.)

How Do I Prepare?

We understand this is a difficult time and support you and your pet. Some owners find it helpful to come to their appointments with a list of questions. Your primary veterinarian can also help you determine what questions to ask.

We will update you on your dog’s status at each appointment. We also discuss recommendations depending on your pet’s response. Treatment plans can change or stop at any point.

Getting Started

Once you have determined the best option, we will work with you to develop an appointment plan. Appointments for patients undergoing treatments and rechecks must be scheduled in advance. All appointments are drop-off appointments.

Drop-offs are between 7:30 am-8:30 am.
Pick-ups occur by 6:00 pm.
No discharges occur between 2:30-3:30 pm as our oncology team is in rounds.
*Costs are estimates. The overall cost depends on patient response. Estimates do not include supportive care or hospitalization.