Introduction
Canine mast cell tumors (MCTs) are abnormal, neoplastic and usually benign accumulations of mast cells that form nodular skin tumors in dogs which, when the mast cells ultimately degenerate, release histamine and other vasoactive substances that can cause or contribute to gastrointestinal (stomach) ulceration, cutaneous (skin) lesions (including pruritus/itchiness) and even systemic clinical signs. Mast cell tumors have the potential to become malignant and often metastasize to other sites. Therefore, they should always be treated immediately when they are found. Treatment options include surgery, radiation, chemotherapy and immunosuppressive steroid administration. The appropriate treatment protocol will depend upon the diagnostic stage of the tumor(s) and your veterinarian’s particular recommendations.
Treating Mast Cell Tumors in Dogs
There is no age or gender predilection for development of mast cell tumors in dogs. However, certain breeds do seem to be predisposed, including the Boxer, Boston terrier, Golden retriever, Labrador retriever, Pug, Shar-pei, Staffordshire bull terrier and Jack Russell terrier. Most cases tend to be diagnosed in older dogs, with a mean age of 8 years, although mast cell tumors have been reported in dogs less than 1 year of age. These masses most often occur in the skin and subcutaneous tissues, and when they metastasize it is to lymph nodes in the region of the primary mass. Thereafter, metastasis normally is to the spleen, liver, mesenteric lymph nodes, other cutaneous (skin) sites and to the bone marrow. The cause of MCT in dogs is unknown.
Canine mast cell tumors can present in a wide variety of ways. They can look like any other skin tumor, lesion or “bump,” including insect bites, skin tags, lipomas or allergic reactions. Usually, mast cell tumors are solitary, although they can occur in multiple places. Most of these tumors are found on a routine veterinary examination, because most dogs show no clinical signs associated with mast cell tumors.
The goal of treating mast cell tumors is to control the local disease or conditions associated with the tumors, and most importantly to prevent metastasis if at all possible. The ultimate goal, even with metastasis, is to maintain or at least manage affected dogs’ quality of life.
Aggressive surgical resection is the primary treatment for mast cell tumors in dogs. Wide surgical margins are recommended, and the resected tissue will be submitted for examination by veterinary pathologists to determine whether appropriate margins were taken during the surgery (i.e., whether enough tissue surrounding the cancer site was removed). Aggressive surgical removal of nearby lymph nodes is also normally done. Follow-up chemotherapy can be useful to prevent or reduce the chances of further metastasis. There are a number of medications that can be prescribed by skilled veterinarians to help manage mast cell cancer after surgical treatment. Radiation therapy can also be very helpful. All new lumps or bumps should be assessed quickly in dogs that have been diagnosed with mast cell neoplasia.
Mast cell tumors of the inguinal, perineal (rear end) and muzzle regions tend to be the most aggressive presentation of this disease. These should always be assessed for potential metastasis.
Pet owners who have dogs that have been diagnosed with mast cell tumors will need to be very vigilant in the future. Owners should learn how to inspect their dog’s skin for any signs of new tumors and need to perform these inspections on a regular basis for the rest of the dog’s life.