01 Nov Mast Cell Staining Variabilities
An 11-year-old spayed female Boston Terrier had a mass removed two months ago, but it was not submitted for histopathologic evaluation. Just caudal to the scar from the previous surgery, a large soft mass is now present, which is possibly the inguinal lymph node. Many large round cells of undetermined origin were noted with in-house, aqueous-based stain (Diff-Quik or similar), see photo A.
The slides stained at the Eastern VetPath cytology laboratory with methanol-based Wright-Giemsa appear differentially (see photo B), and consist of many moderately granulated mast cells of variable size, with fewer small lymphocytes, occasional plasma cells, and occasional eosinophils. Scattered purple granules are also present in the background.
Likely due to the biologic behavior of this metastatic mast cell population, and the aqueous-based in-house staining, these mast cells did not exhibit granulation in photo A, making the diagnosis difficult. This case reaffirms the importance of submitting unstained slides, along with previously stained slides, whenever possible. The methanolic-based stains that many pathology laboratories use can stain many granulated cells differently than stains used in a veterinary hospital (water-diluted stain solutions can wash away granules contents).