Non-staining Intraabdominal Mast Cell Tumor in a Cat

History: 9-year-old cat, domestic short hair, intact female , having a 2 x 4 cm nodular palpable mass in dorsal/mid abdomen.

Cytological description: The images contain a background of erythrocytes with multiple medium-sized discrete round cells. These are characterized by a moderate amount of pale basophilic cytoplasm with multiple small clear round vacuoles, one small to medium-sized round to oval nucleus with fine granular chromatin, occasional poorly-defined nucleoli, and mild to moderate anisocytosis and anisokaryosis. There is moderate to severe infiltration by eosinophils.

Comments: The small intracytoplasmic vacuoles are in fact non-staining mast cell granules. These non-staining mast cells tumors represent a small percentage of mast cell neoplasms. If the mass originates from the spleen, splenectomy is usually associated with prolonged survival. If the mass appears to be of intestinal origin, these have a higher tendency for widespread metastasis and are usually associated with a poorer prognosis.

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