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.