Mast cell tumors are the most common skin tumors in dogs, developing from abnormal growth of mast cells, which are normally involved in allergic and immune responses. Treatment depends on tumor grade, size, and spread, ranging from surgery to radiation therapy to systemic therapies like chemotherapy and/or targeted therapy. Low-grade tumors that are completely removed with surgery carry the best prognosis while high-grade or metastatic tumors often require therapy beyond surgery and carry a more guarded prognosis. As always, consulting a veterinarian or veterinary oncologist is recommended for staging and personalized treatment planning.
Mast cells are large cells that contain histamine and heparin granules and are normally found throughout the body, including the skin. Mast cells play a crucial role in allergic and immune responses and tumors develop when these cells grow abnormally.
Mast cell tumors primarily affect older dogs, with an average age of 8-9 years, but they have also been reported in younger dogs. Certain breeds are at an increased risk, including Boxers, Boston Terriers, Bulldogs, Labrador and Golden Retrievers, Staffordshire Terriers, and Shar Peis. Interestingly, while brachycephalic breeds have a higher risk of developing mast cell tumors, their tumors tend to be low to intermediate grade.
Treatment Options
The treatment approach for mast cell tumors depends on several factors, including size, location, presence of metastasis, and tumor grade. If the tumor can be fully removed through surgery, that is the preferred treatment option. If clean margins cannot be achieved with surgery alone, radiation therapy can be used following surgery to prevent tumor recurrence. In cases where surgery is not an option, radiation therapy can be used as a palliative approach to potentially shrink the mass and delay further growth.
Chemotherapy is often recommended for high-grade mast cell tumors, either as a standalone treatment or following local therapy such as surgery or radiation. Commonly used chemotherapy drugs for mast cell tumors include vinblastine and lomustine. While dogs generally tolerate chemotherapy well, side effects can occur, including lethargy, decreased appetite, vomiting, diarrhea, and a reduced white blood cell count. As part of the chemotherapy protocol for mast cell tumors, veterinarians sometimes prescribe an oral steroid called Prednisone. This medication is also generally well-tolerated, though it may cause side effects such as increased thirst, urination, hunger, and panting.
Beyond conventional chemotherapy, targeted therapy is commonly used for high-grade or recurrent mast cell tumors. The targeted therapy, Palladia, was designed to attack mutations in a gene called c-KIT which is commonly mutated in high-grade mast cell tumors. In addition to Palladia, FidoCure enables access to additional targeted therapies that may target other identified mutations. These are all oral medications administered at home and require routine check-ups to ensure tolerability and efficacy.
Prognosis
A key prognostic factor for mast cell tumors is the tumor grade, which can only be determined by a biopsy after the tumor is removed. For the most accurate prognosis and treatment recommendations for your dog with mast cell tumors, consult your veterinarian or a veterinary oncologist. They can provide personalized guidance based on your dog's specific case, considering factors such as cancer stage, grade, tumor location, and concurrent health issues.