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Case 120 - Discussion

Hematopathology Case

Systemic mastocytosis in the marrow typically present with nodular or sheets of infiltration . The nodules consist of spindle  cells with surrounding reactive lymphocytes and eosinophils. Sometimes, the tumor cells show paratrabecular infiltration with prominent fibrosis, closely resembling collagen fibrosis. Occasionally, hairy cell leukemia cells may display short spindle morphology, mimicking mast cells.

Systemic Mastocytosis

  • Classification:

    • Cutaneous mastocytosis: mostly urticaria pigmentosa (UP) in children. Less commonly telangiectasia macularis eruptiva perstans (TMEP) in adults.
    • Indolent systemic mastocytosis
    • Systemic mastocytosis with associated clonal hemtological non-mast-cell lineage diease
    • Aggressive systemic mastocytosis
    • Mast cell leukemia
    • Mast cell sarcoma
    • Extracutaneous mastocytoma
  • Criteria for systemic mastocytosis: one major and one minor or at least three criteria
    • Major criteria: multifocal dense infiltrates of mast cells of at least 15 cells
    • Minor criteria:
      • > 25% mast cells are spindle, atypical or immature
      • Condon 816 mutation of c-Kit
      • CD2+ and/or CD25+
      • Serum tryptase > 25 ng/ml
  • Morphology

    • Cohesive aggregates of mast cells with short spindle nuclei, blunt ends, open chromatin. Cytoplasm is pale pink and blue.

    • Lymphoid aggregates

    • Mixed eosinophils

  • Special stains

    • CAE (naphthol-ASD-chloroacetate esterase) +

    • Giemsa or toluidine blue

  • Immunostains: CD117+, CD2+, CD25+, tryptase+, chymase+, CD45+, CD68+, CD14-, CD16-

  • Genetics: point mutation of c-Kit, mostly codon 816 in the tyrosine kinase domain.

Reference: Swerdlow, S.H., Campo, E., Harris, N.L., Jaffe, E.S., Pileri, S.A., Stein, H., Thiele, J., Vardiman, J.W. WHO Classification of Tumours of Haematopoietic and Lymphoid Tissues, Fourth Edition. 2008.