Acute mast cell leukemia. (A and B) Blood film. Occasional blast cells (no granules) and frequent mast cells at diagnosis as shown here. Blast cells increased in later blood films. (C) Marrow biopsy. Diffusely infiltrated with mast cells that also formed focal aggregates. The marrow biopsy was hypercellular and contained 29% of cells with mast cell granules and 7% blast cells (no granules). Vertical arrow indicates one of several blast cells. (D) The mast cells vary in maturity from early myelocytes (often with nucleoli and immature chromatin patterns) but with a few large mast cell granules to mature mast cells (horizontal arrow). Many of the mast cells have multilobed nuclei and atypical granules. The leukemic mast cells were positive for CD117, CD25, and tryptase. The flow cytometric phenotype of the blast cells was slightly different from the mast cells in that it CD34-positive but CD25-negative, whereas the mast cells were CD34-negative and CD25-positive. CD117 was much stronger in the mast cells than in the blast population.
Acute mast cell leukemia: Marrow immunocytostains. Marrow biopsy. The marrow aspirate is hypercellular and contains 29% cells with mast cell granules and 7% blasts (no granules). The mast cells vary in maturity from early myelocytes (often with nucleoli and immature chromatin patterns) but with a few large mast cell granules through to mature mast cells. The brown cytoplasmic staining of marrow cells indicates a positive immunological reaction for (A) CD25, (B) CD117, and (C) tryptase. The latter is a specific marker for mast cells granules.
Mastocytosis with eosinophilia. 38 year old man with mild anemia, normal platelet count and a white cell count of 61.6 x 109/L with 30% eosinophils and 1.8% basophils. (A) Blood film showing striking eosinophilia. Many of the eosinophils were atypical with three nuclear segments or an occasional circular nucleus. Infrequent myelocytes were noted but no increase in blast cells in blood. (B)Marrow biopsy was hypercellular (100% cellularity) with intense infiltrate of eosinophils, grade 3 reticulin fibrosis, and frequent areas of mast cell infiltrates. No increase in blast cells. (C) Area of mast cell infiltrate in marrow admixed with eosinophils. The mast cells were atypical in appearance being spindle-shaped and with fewer cytoplasmic granules (D). Tryptase stain confirming mast cell infiltrates in marrow. This case could also be considered chronic eosinophilic leukemia with associated mast cell disease.
Systemic mastocytosis. Marrow section. Arrows point to clusters of mast cells stained dark blue.