Clinical Rounds: Recurrent mast cell tumors in a boxer
Make the rounds with these veterinary specialists and residents and see how various combinations of therapy eventually produced a good outcome in this case.
Cytologic samples from canine mast cell tumors are typically highly cellular and have a predominance of granulated mast cells
(round to oval cells with abundant, fine to coarse, metachromatic cytoplasmic granules). Mast cells may be present individually
or in aggregates and may be associated with low to moderate numbers of scattered eosinophils and plump, often pleomorphic,
fusiform cells. The background of the smear often contains blood and variable numbers of scattered mast cell granules from
ruptured cells.
Samples containing a highly mixed population of cells and those obtained from noncutaneous lesions (e.g. spleen, lymph node) should be interpreted cautiously, as moderate or sometimes high numbers of mast cells may be present as
part of a reactive or inflammatory process. Many resources that may aid in cytologic evaluation of canine cutaneous mast cell
tumors are available.14 Canine cutaneous mast cell tumors are graded based on histopathologic not cytopathologic criteria (see anatomic pathology
perspective).
2. This fine-needle aspirate from a cutaneous axillary mass in a dog contains individualized round cells with low numbers
of scattered eosinophils and neutrophils and a small amount of blood. The round cells are large with pale cytoplasm, which
frequently contains a moderate amount of fine, faint metachromatic granulation. They demonstrate moderate anisocytosis and
anisokaryosis, and occasional binucleation (inset) (Wright’s stain [aqueous], 100X).
When mast cells are heavily granulated and present in high numbers, cytologic interpretation is not challenging. However,
some mast cell tumor samples may contain cells with few or faint granules, which may reflect poor differentiation of the neoplastic
cells or may be associated with staining methodology. Mast cell granules may stain poorly or not at all when an aqueous-based
stain such as a modified Wright's stain (Diff Quik—Dade Behring) or most other dip stains is used.15
This case
Fine-needle aspiration of multiple skin lesions and a lymph node in the dog in this case revealed a predominance of large,
pale round cells with variable amounts of very fine, faint cytoplasmic granulation (Figure 2).
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