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Mastocytosis represents a group of disorders associated with a neoplastic proliferation of mast cells in one or more organ systems. This myeloproliferative neoplasm is further subtyped into cutaneous (involving skin lesions) and systemic (multifocal lesions in bone marrow or various other organs) mastocytosis.
The majority of patients with systemic mastocytosis possess the genetic mutation D816V in the KIT gene.
The World Health Organization (WHO) recommends this diagnostic criteria for systemic mastocytosis:
Diagnosis can be made when the major criterion and one minor criterion or at least three minor criteria are present
Major criterion:
  • Infiltrates of mast cells (more than 15 mast cells in aggregates) detected in sections of bone marrow and/or other organ(s)
Minor criteria:
  • In biopsy section, more than 25% of the masts cells in the infiltrate have atypical morphology, or, of all the mast cells in the aspirate smear, more than 25% are immature or atypical
  • Mast cells co-express CD117 with CD2 and/or CD25
  • Detection of KIT point mutation at codon 816 in bone marrow, blood, or other organs
  • Serum total tryptase persistently >20 ng/ml (not a valid criteria in cases of systemic mastocytosis with associated clonal hematologic non-mast-cell lineage disease)