A mast cell tumor in dogs is a cancerous neoplasm of mast cells. Mast cells are immune system cells that release histamine and other substances in response to certain stimuli, such as allergens or parasites. When mast cells become cancerous they can secrete potent substances that can cause tissue damage and interfere with the body’s ability to heal itself. A mast cell tumor is the most common cutaneous cancer in dogs. The vast majority of mast cell tumors in dogs are a result of a genetic mutation that causes mast cells to grow uncontrollably. This article will discuss what mast cell tumors are in dogs and how they are treated.
What are the normal functions of a mast cell?
Mast cells are a type of immune cell that is found in most tissues of the body. They play an important role in the immune system by defending the body against infection and helping to heal wounds. Mast cells also release histamine and other substances in response to certain stimuli, such as allergens or parasites. Histamine is responsible for many of the symptoms of an allergic reaction, such as itching and swelling.
What is a mast cell tumor in dogs?
Mast cell tumors are a type of cancer that arises from mast cells. When mast cells become cancerous they can secrete potent substances that can cause tissue damage and interfere with the body’s healing ability. Mast cell tumors are the most common cutaneous cancer in dogs and originate from the skin or subcutaneous tissues. The cause of mast cell tumors in dogs is largely unknown, but it is believed that they may be caused by a genetic mutation that causes mast cells to grow uncontrollably. Mast cell tumors are most common in older dogs (average age of 8-9 years) and frequently affect Boxers, pugs, Boston terriers, golden retrievers and English bulldogs.
What are the grades of a mast cell tumor in dogs?
Mast cell tumors in dogs are staged from I to IV:
- Grade I: A localized tumor confined to the skin without lymph node involvement and a low mitotic rate. This is the most favorable grade and has a high cure rate with surgery alone.
- Grade II: The tumor is larger than Grade I and may have regional lymph node involvement but still has a low mitotic rate.
- Grade III: The tumor is large, often ulcerated, and has a high mitotic rate. This grade has a poor prognosis with surgery alone. There are often multiple mast cell tumors present.
- Grade IV: Any mast cell tumor with metastasis to other parts of the body, and has a high mitotic rate. This grade has a very poor prognosis.
What are the clinical signs of a mast cell tumor in dogs?
Mast cell tumors in dogs have a wide variation in their clinical appearance. Most mast cells are single and found on the surface of your skin or deeper inside you like under your skin, while up to 15% of dogs with mast cell tumors have more than one lesion. Well-differentiated masses tend to be small and slow-growing, being covered by hair but not open sores; whereas undifferentiated masses grow quickly, ulcerate (open up into wounds), and may cause surrounding tissues to become inflamed due to swelling or spontaneously in response to injury. This can change how often an area is swollen which causes the tumor size change as well. It's important for owners who notice these symptoms that they alert their veterinarian so they can treat this condition properly before it worsens.
Large mast cell tumor burdens in some dogs can result in signs related to the release of mast cell mediators. The signs may include vomiting, diarrhea, peripheral edema (swelling), fever, and collapse.
How is a mast cell tumor in dogs diagnosed?
A mast cell tumor in dogs is diagnosed by your veterinarian after a physical examination and review of the medical history. Mast cell tumors vary widely in appearance and can mimic almost any other skin or subcutaneous lesion and they are often white, pink, or tan in color. In contrast to well-differentiated canine mast cell tumors, which are solitary, small masses that grow slowly and typically do not ulcerate. Aggressive, undifferentiated canine mast cell tumors often grow rapidly and also ulcerate more frequently. Mast cell tumors in dogs can occur anywhere on the body but have no consistent site predilection.
Cytology is often recommended and performed by your veterinarian. Cytology can provide pertinent amounts of information while being non-invasive and inexpensive. Cytology is a microscopic examination of cells that have been removed from the body. The cells are placed on a glass slide and stained with dye. The stained cells are then examined under a microscope. A mast cell tumor will typically have many and an abundance of mast cells with varying appearances. As mast cell tumors contain high numbers of mast cells that release histamine, giving an antihistamine such as diphenhydramine (Benaryl®) prior to sampling may help reduce side effects.
The most consistent and dependable predictor of a mast cell tumor in dogs is histopathology, however, it does not always accurately forecast the behavior of every tumor. Histopathology is the microscopic examination of tissues that have been removed from the body. The tissues are placed on a glass slide, stained with dye, and then examined under a microscope by a pathologist. Histopathology is most commonly performed after the mast cell tumor has been surgically removed. Histopathology can provide information on the stage of the mast cell tumor and if there is likely to be recurrence based on the surgical removal.
What are the treatment options for a mast cell tumor in dogs?
The treatment options for mast cell tumors in dogs include surgery, radiation therapy, TKI therapy, and chemotherapy.
Grade I and II mast cell tumors that are localized to the skin can often be treated with surgery alone. Grade III mast cell tumors are often treated with a combination of surgery, chemotherapy, and radiation. Grade IV mast cell tumors are typically treated with radiation therapy and chemotherapy.
Surgery
In most cases of mast cell tumors in dogs, surgery is the primary treatment. Cytologically confirmed mast cell tumors are surgically excised with wide margins. When your veterinarian is surgically removing a suspected mast cell tumor, wide margins mean your veterinarian will remove 2-3cm of tissue around and beneath the mast cell tumor. This technique will help prevent any future recurrence in that location.
Radiation Therapy
Radiation therapy is usually reserved for tumors that cannot be removed via wide excision due to anatomic limitations or for cases in which local lymph nodes are affected by high-grade mast cell tumors.
Tyrosine Kinase Inhibitors (TKIs)
As opposed to standard chemotherapy, Palladia® forges the way in a new approach to the treatment of cancer known as “targeted therapy.” This process focuses on solving specific issues related to your kind of cancer by attacking only specific receptors on the surface of your cancer cells and blood vessels where they're most vulnerable. Palladia® is FDA-approved for use in the treatment of mast cell tumors in dogs.
Chemotherapy
Chemotherapy after surgery is usually reserved only for dogs with metastatic disease or when metastatic disease is suspected.
What is the prognosis for a mast cell tumor in dogs?
The prognosis for mast cell tumors in dogs varies depending on the grade of the tumor. The majority of mast cell tumors in dogs are a result of a genetic mutation and are not curable, but the prognosis is much better for those with lower grades (I and II). Dogs with mast cell tumors that have metastasized to other parts of the body have a very poor prognosis. It is important for owners of dogs with mast cell tumors to seek treatment from a veterinarian who has experience treating this type of cancer.
In summary, a mast cell tumor in dogs is the most common cutaneous neoplasm, and it is largely caused by a genetic mutation. Treatment options include surgery, radiation therapy, TKI therapy, and chemotherapy. Grade I and II mast cell tumors that are localized to the skin can often be treated with surgery alone, while grade III mast cell tumors are often treated with a combination of surgery, radiation therapy, and chemotherapy. Grade IV mast cell tumors are typically treated with radiation therapy and chemotherapy. The prognosis for mast cell tumors in dogs varies depending on the grade of the tumor but most cutaneous mast cell tumors behave benignly.