In most species, neoplastic processes involving mast cells are relatively uncommon. In contrast, mast cell tumors (MCTs) occur frequently in the pet population, representing up to 20% of all cutaneous canine tumors [1-3]. As such, a detailed comprehension of the diagnosis and treatment of mast cell neoplasia in the dog is extremely important. Before discussing the specifics of MCTs, however, it is first necessary to understand normal mast cell biology.
Mast cell biology
Morphologic characteristics of mast cells
Mast cells are discrete round cells roughly one to three times the size of a neutrophil. They possess a round to oval nucleus and distinct cytoplasmic granules that stain with dyes, such as toluidine blue, Giemsa, and methylene blue. Such staining is a result of the affinity of these basic dyes for the acidic proteoglycans contained in the mast cell granules [4][5][6][7]. Some of these dyes assume a different color when bound by the granules than they do when staining nuclear DNA, so that the granules are often called metachromatic. Although mast cells may be visualized on hematoxylin and eosin-stained sections, the dyes described previously are used to characterize mast cells definitively. Moreover, mast cell granules may not be visualized with stains like Diff-Quick (Dade Behring, Deerfield, IL), precluding identification on some cytologic specimens [8].
Development of mast cells
Mast cells are derived from bone marrow precursor cells. They leave the bone marrow in a presumed immature state and migrate to many Vet Clin Small Anim 33 (2003) 473-489