Canine Mast Cell Tumors

At Animal Cancer Care Clinic (ACCC), we understand that discovering a lump or bump on your dog and receiving a diagnosis of a mast cell tumor can be concerning. Please know that our experienced and compassionate team is here to support you and your furry companion every step of the way. Mast cell tumors are the most common skin tumors in dogs, and while they can vary significantly in their behavior, we have a range of diagnostic and treatment options available at ACCC to help manage this condition and maintain your dog’s quality of life.

What are Mast Cell Tumors?

Mast cells are a type of white blood cell that are normally involved in the body’s immune response, particularly in allergic reactions and inflammation. They contain granules filled with various substances, such as histamine, heparin, and other enzymes. A mast cell tumor occurs when these mast cells grow uncontrollably and form a mass.

It’s important to understand that mast cells are found throughout the body, not just in the skin. While skin mast cell tumors are the most common, they can also occur internally in organs like the spleen, liver, and bone marrow, although this is less frequent.

The behavior of mast cell tumors can be unpredictable. Some may be slow-growing and relatively benign, while others can be aggressive, grow rapidly, and spread (metastasize) to other parts of the body.

What Causes Mast Cell Tumors in Dogs?

The exact cause of mast cell tumors in dogs is not fully understood in most cases. However, research suggests that several factors may play a role:

Genetics: Certain breeds, such as Boxers, Boston Terriers, Bulldogs, Pugs, Rhodesian Ridgebacks, and Shar-Peis, have a higher incidence of mast cell tumors, indicating a genetic predisposition.
Chronic Inflammation: Some theories suggest that chronic skin irritation or inflammation might contribute to the development of mast cell tumors in certain areas.
Growth Factors: Abnormalities in certain growth factors and their receptors within mast cells may contribute to their uncontrolled growth.

Mast cell tumors are generally not contagious to other pets or humans.

Signs and Symptoms of Mast Cell Tumors:

The appearance and symptoms of mast cell tumors in dogs can be highly variable:

Skin Lumps or Bumps: This is the most common presentation. These lumps can vary greatly in size, shape, and texture. They may be small or large, firm or soft, raised or flat, and may or may not be ulcerated (open and bleeding). Some tumors may appear and disappear or fluctuate in size due to the release of their granule contents.
Swelling or Redness: The area around the tumor may be swollen or red, sometimes due to inflammation caused by the release of mast cell granules.
Itching or Irritation: The tumor site may be itchy, and your dog may lick or chew at it, further irritating the area and potentially causing self-trauma.
Gastrointestinal Upset: In some cases, the release of histamine and other substances from the mast cells can lead to gastrointestinal signs such as vomiting, diarrhea, and loss of appetite. In rare, severe cases, this can even lead to gastric ulcers.
Enlarged Lymph Nodes: If the mast cell tumor has spread to the regional lymph nodes, you may notice them becoming enlarged.
Systemic Signs (Less Common): In advanced cases where the tumor has spread to internal organs, your dog may exhibit more generalized signs such as lethargy, weight loss, and abdominal enlargement.

Due to the variable appearance of mast cell tumors, it’s important to have any new or changing lumps or bumps on your dog examined by a veterinarian.

How are Mast Cell Tumors Diagnosed?

Diagnosing mast cell tumors typically involves several steps:

Physical Examination: A veterinarian will perform a thorough physical examination of your dog, paying close attention to any skin masses and palpating the regional lymph nodes.
Fine Needle Aspirate (FNA): This is the most common initial diagnostic test for a suspected mast cell tumor. A small needle is inserted into the mass to collect a sample of cells, which are then examined under a microscope (cytology). FNA can often provide a preliminary diagnosis of a mast cell tumor.
Biopsy: A biopsy involves taking a larger tissue sample of the mass, which is then sent to a pathologist for a more detailed examination (histopathology). Biopsy is crucial for determining the grade of the mast cell tumor, which is a significant factor in predicting its behavior and guiding treatment decisions. Biopsies can be obtained through surgical removal (excisional biopsy) or by taking a smaller wedge of tissue (incisional biopsy).
Lymph Node Aspirate: If the lymph nodes near the tumor are enlarged, a veterinarian may perform an FNA of the lymph node to check for spread (metastasis).
Blood Work: A complete blood count (CBC) and serum chemistry panel are typically performed to assess your dog’s overall health and to look for any signs of systemic involvement.
Imaging (Radiographs/X-Rays, Ultrasound): Depending on the grade and location of the tumor, imaging studies, such as chest radiographs or abdominal ultrasound, may be recommended to check for spread to internal organs.
Bone Marrow Aspirate (Less Common to Rt6are): In cases of high-grade tumors or suspicion of bone marrow involvement, a bone marrow aspirate may be recommended.

Grading of Mast Cell Tumors:

The grade of a mast cell tumor, determined by the pathologist after examining the biopsy sample, is a critical factor in predicting its behavior (aggressiveness and likelihood of metastasis) and guiding treatment. There are currently two grading systems in use:

Patnaik Grading System:
- Grade I (Low Grade): These tumors are generally less aggressive and have a lower risk of spreading. They are often curable with complete surgical removal.
- Grade II (Intermediate Grade): These tumors have a more variable behavior. Some may behave like grade I tumors, while others can be more aggressive and have a higher risk of local recurrence or metastasis.
- Grade III (High Grade): These tumors are the most aggressive and have a high risk of local recurrence and metastasis to regional lymph nodes and distant organs.
Kiupel Grading System:
- Low grade: These tumors are generally less aggressive and have a lower risk of spreading. They may be curable with complete surgical removal.
- High grade: These tumors are the most aggressive and have a high risk of local recurrence and metastasis to regional lymph nodes and distant organs.

Treatment Options for Canine Mast Cell Tumors:

At Animal Cancer Care Clinic, we offer a comprehensive range of treatment options for canine mast cell tumors, tailored to the grade, location, and extent of the tumor, as well as your dog’s overall health and your individual goals.

Surgery: Surgical removal is the primary treatment for many mast cell tumors, especially low-grade (grade I) and some intermediate-grade (grade II) tumors. Achieving wide surgical margins (removing a significant amount of normal tissue around the tumor) is crucial to prevent local recurrence. Our skilled surgeons at ACCC are experienced in performing these delicate procedures.
Radiation Therapy: Radiation therapy may be used in cases where complete surgical removal is not possible, or for high-grade tumors or those with microscopic disease remaining after surgery. It can help to control local tumor growth and prevent recurrence.
Chemotherapy: Chemotherapy is often recommended for high-grade (grade III) mast cell tumors or for cases where there is evidence of spread to regional lymph nodes or distant organs. Various chemotherapy protocols are available, and our veterinary oncologists at ACCC will develop a personalized plan for your dog.
Tyrosine Kinase Inhibitors (TKIs): These are oral medications that target specific proteins involved in the growth and survival of mast cells. TKIs, such as toceranib (Palladia), can be effective in treating some mast cell tumors, particularly higher-grade or metastatic disease. They can be used alone or in combination with other therapies.
Steroids (Corticosteroids): Medications like prednisone can help to reduce inflammation associated with mast cell tumors and may have some direct anti-tumor effects. They are often used as part of a treatment plan or for palliative care.
Cryosurgery: Freezing the tumor may be considered for smaller or superficial tumors.
Electrochemotherapy (ECT): ECT can be used on the scar of a mast cell tumor that was not completely removed with surgery to help prevent regrowth of the cancer.
Stelfonta: Stelfonta is a compound isolated from a plant seed that can help to kill a mast cell tumor when injected directly into the tumor.
Supportive Care: Managing the effects of mast cell degranulation (release of granule contents) is important. Antihistamines (H1 and H2 blockers) and gastroprotectants are often used to minimize gastrointestinal upset and other systemic signs.

What to Expect During and After Treatment:

If your dog undergoes treatment for a mast cell tumor at ACCC, regular veterinary visits and monitoring will be essential. Our dedicated team will closely monitor their response to therapy and manage any potential side effects with the utmost care.

Post-surgical care will involve ensuring proper wound healing and monitoring for any signs of local recurrence. For dogs receiving chemotherapy or TKIs, we will closely monitor their blood work and overall well-being.

Long-term monitoring for recurrence or metastasis is crucial for dogs with mast cell tumors. This may involve regular physical examinations, lymph node checks, and potentially imaging studies.

Prognosis for Canine Mast Cell Tumors:

The prognosis for dogs with mast cell tumors varies significantly depending on several factors, including:

Grade of the Tumor: Grade I tumors generally have an excellent prognosis with complete surgical removal. Grade III tumors have a more guarded prognosis due to their higher risk of recurrence and metastasis. Grade II tumors have a variable prognosis.
Surgical Margins: Achieving wide and clean surgical margins significantly improves the prognosis for surgically treated tumors.
Location of the Tumor: Tumors in certain locations (e.g. mucocutaneous junctions, nail bed) can be more challenging to treat and may have a less favorable prognosis.
Presence of Metastasis: If the tumor has already spread to regional lymph nodes or distant organs, the prognosis is less favorable.
Response to Treatment: How well the tumor responds to surgery, radiation therapy, chemotherapy, or TKIs can influence the long-term outcome.

We will discuss the potential prognosis for your dog based on their specific diagnosis and treatment plan. While we will be honest about the challenges, we are also committed to providing the best possible care to improve their quality of life and extend their survival.

Coping with a Mast Cell Tumor Diagnosis:

Receiving a diagnosis of a mast cell tumor for your dog can be a source of anxiety and uncertainty. Please know that the team at ACCC is here to provide not only expert medical care for your dog but also compassionate support for you during this time.

We encourage you to ask us any questions you have and to share your concerns openly. We want you to feel informed and empowered as you make decisions about your dog’s care. We can also provide information about resources that may be helpful for pet owners dealing with cancer.

Our goal is to work with you to develop a treatment plan that is tailored to your dog’s needs and your wishes, while always prioritizing their comfort and well-being.

Questions to Ask Your Veterinarian:

To help you better understand your dog’s condition and the treatment options available at Animal Cancer Care Clinic, here are some questions you may find helpful to ask us:

What grade is my dog’s mast cell tumor?
What are all the treatment options available for my dog’s tumor based on its grade and location?
What are the goals of each treatment option?
What are the potential side effects of the recommended treatment plan? How will these be managed?
What is the expected prognosis for my dog with the recommended treatment?
What are the chances of local recurrence or metastasis?
How will my dog be monitored for recurrence or spread?
What is the estimated cost of the recommended treatment plan and ongoing care?
What can I do at home to best support my dog during and after treatment?

Conclusion:

At Animal Cancer Care Clinic, we are dedicated to providing the highest level of care for dogs with mast cell tumors. Our experienced team will work closely with you to develop a personalized treatment plan and provide ongoing support for you and your beloved companion. Please do not hesitate to reach out to us with any questions or concerns you may have. We are here to help you navigate this journey.