Mast cell tumors (MCTs) can be benign. However, they have the potential to become malignant and often metastasize to sites other than the skin. Therefore, any skin lump should always be assessed by a veterinarian and, if found to be a mast cell tumor, treated immediately. The goals of treating mast cell tumors are to control the local disease or other conditions associated with the tumors, and most importantly to prevent metastasis if at all possible. The ultimate goal, even with metastasis, is to improve, maintain or at least manage the affected dog’s quality of life.
Treatment options include surgery, radiation therapy, chemotherapy and immunosuppressive steroid administration. Veterinarians will stage mast cell tumors based on their size, number, degree of local involvement and presence or absence of metastasis. The appropriate treatment protocol will depend upon the diagnostic stage of the tumor(s) and the attending veterinarian’s particular preferences and recommendations. Mast cell tumors of the prepuce, scrotum, perineal area (around the anus), toes (digits), ear flaps (pinnae), ear canal, oral mucosa (gums) and muzzle tend to be the most aggressive. These should always be assessed for potential metastasis.
Aggressive surgical resection is the primary treatment for MCTs in dogs. Wide surgical margins are recommended, and the resected tissue will be submitted for examination by a veterinary pathologist to determine whether sufficient surgical margins were achieved (that is, whether enough normal tissue around the tumor was removed, to be certain that all cancerous tissue at that site was removed). Nearby lymph nodes are also normally removed surgically, because they typically are the first place where the mast cell neoplasia will spread.
For early-stage tumors, surgical excision of the entire mass with normal margins of healthy tissue around the mass is the treatment of choice and is usually highly successful. Larger tumors, or tumors that are located in areas where removal with good margins is not possible, typically are treated by surgical resection of as much of the mass and margins as possible, followed by radiation, chemotherapy and/or immunotherapy.
Chemotherapy can be helpful for many dogs treated surgically for mast cell cancer, to prevent or reduce the chances of further metastasis. There are a number of chemotherapeutic drugs that can be prescribed and administered by skilled veterinarians to help manage mast cell cancer post-operatively. Radiation therapy can also be very helpful to affected dogs. All new lumps or bumps should be assessed quickly in dogs that previously have been diagnosed with mast cell neoplasia.
Prognosis for Dogs with Mast Cell Tumors
The outlook for dogs with mast cell tumors depends on how advanced the disease is at the time it is diagnosed and treated. Dogs with mast cell tumors graded in the early stages usually have a very good to excellent prognosis with appropriate treatment, while mast cell tumors in the later stage have a guarded to grave prognosis, depending upon the nature and extent of metastasis and the dog’s response to chemotherapy and radiation treatments. Owners of dogs that have been diagnosed with mast cell tumors must be vigilant in the future and should regularly inspect the skin on their dog’s entire body for any signs of new tumors. This should be done for the rest of the dog’s life.