Mast Cell Tumours: New Grading, New Treatments

摘要

In dogs, mast cell tumours (MCTs) are most commonly found in the cutaneous tissue; and this is the most common malignancy of the skin in dogs. In most dogs, tumours are solitary, but in about 10 - 15%, the tumours are multiple. Tumours usually occur in older dogs (mean age 9 years) with no sex predilection. Boxers, Rhodesian ridgebacks, pugs, Boston terriers, pit-bull terriers and Weimaraners are at high risk (4 to 8 times more than the general population) for developing MCTs. Shar-Peis, particularlyyoung dogs, are predisposed to developing MCT, and these tumours are often poorly differentiated and biologically aggressive.It is uncommon to diagnose MCTs without skin involvement in dogs. Mast cell tumours vary greatly in appearance, and no estimate of their malignancy or prediction of their behavior can be made on clinical appearance alone. Some MCTs may be present for months to years before rapidly disseminating; others act aggressively from the beginning. Occasionally, mechanical manipulation during examination of this tumour causes degranulation of mast cells, producing erythema and wheal formations. This phenomenon has been observed in both dogs and cats (the "Darier's sign") and is considered of diagnostic significance. Owners may report that the tumour enlarges rapidly and then diminishes in size over a period of about 24 hours. Such a history should increase the clinician's suspicion of mast cell tumour.The clinical appearance of MCTs in dogs may vary widely but diagnosis is relatively easy using aspiration cytology. Presurgical aspiration of these tumours provides a cytology specimen characterized by round cells that may have well-stained and large cytoplasmic granules (well-differentiated) or that may be more anaplastic with small, poorly staining cytoplasmic granules. Eosinophils are often seen in aspirates of MCTs because of eosinophil chemotaxis to histamine release.