Oncology
Mast Cell Tumors in Dogs
What are Mast Cell Tumors?
Mast cell tumors are one of the most common skin tumors in dogs. They are highly variable in appearance. We recommend that all masses be evaluated with fine needle aspiration cytology which can readily diagnose most mast cell tumors as well as a variety of other tumors. Once a mast cell tumor is identified, we recommend that a biopsy be performed to confirm the diagnosis and determine the tumor "grade." The specific behavior, treatment recommendations and prognosis correlate with the grade of the tumor.
Tumor Grades/Diagnostic Testing
Grade I mast cell tumors are minimally invasive and spread to other places in the body (called metastasis) is not expected. Wide surgical excision should be curative.
Grade II mast cell tumors are invasive into adjacent tissues, although again, metastasis is uncommon. Diagnostic tests are recommended to ensure there is no obvious evidence of spread to other places in the body. These tests include:
- Complete blood count (CBC)
- Serum biochemistry panel
- Urinalysis (U/A)
- Lymph node aspiration cytology
- Abdominal sonogram
Wide and complete surgical excision is the treatment of choice. If this is not possible, the combination of surgery (to remove obvious gross disease) followed by radiation therapy (to destroy residual microscopic disease) is very effective. This combination is associated with a 95% chance of 1-year tumor control and an approximately 85-95% chance of 2-5 year control.
Grade III mast cell tumors are locally invasive and differ from grade II tumors in having a moderate-high rate of metastasis. Diagnostic tests are recommended to ensure there is no obvious evidence of spread to other places in the body. These tests include:
- Complete blood count (CBC)
- Serum biochemistry panel
- Urinalysis (U/A)
- Lymph node aspiration cytology
- Abdominal sonogram
- Liver aspiration cytology
- Spleen aspiration cytology
- Buffy coat prep
- Bone marrow aspiration cytology
Treatment
Treatment ideally consists of local therapy as described for grade II mast cell tumors combined with systemic chemotherapy aimed at delaying or preventing the onset of metastatic disease. Our current protocol involves a combination of prednisone, vinblastine, and CCNU, the three drugs with demonstrated effectiveness against mast cell tumors. Chemotherapy can also be used alone if surgery and radiation therapy are not performed. Mast cells contain and can release numerous granules (e.g. histamine) and when present in high concentrations, these substances can become irritating to the stomach and other organs. To protect the body from these granules, we recommend that dogs with grade III mast cell tumors be treated continuously with both H1 (diphenhydramine) and H2 (cimetidine, famotidine, or ranitidine) receptor antagonists.
Selected References
- Al-Sarraf R, Mauldin GN, Patnaik AK , et al. A prospective study of radiation therapy for the treatment of grade 2 mast cell tumors in 32 dogs. J Vet Int Med 1996;10:376-378.
- Frimberger AE, Moore AS , LaRue SM, et al. Radiotherapy of incompletely resected, moderately differentiated mast cell tumors in the dog: 37 cases (1989-1993). J Am Anim Hosp Assoc 1997;33:320-324.
- LaDue T, Price GS, Dodge R, et al. Radiation therapy for incompletely resected canine mast cell tumors. Vet Radiol Ultrasound 1998;39:57-62.
- McCaw DL, Miller MA, Ogilvie GK, et al. Response of canine mast cell tumors to treatment with oral prednisone. J Vet Int Med 1994;8:406-408.
- Rassnick KM, Moore AS , Williams LE, et al. Treatment of canine mast cell tumors with CCNU (lomustine). J Vet Int Med 1999;13:601-605.
- Thamm DH, Mauldin EA, Vail DM. Prednisone and vinblastine chemotherapy for canine mast cell tumor - 41 cases (1992-1997). J Vet Int Med 1999;13:491-497.