Chronic myeloid neoplasms
Mast Cell Neoplasm

Topic Completed: 1 August 2011

Revised: 5 March 2020

Copyright: 2002-2020,, Inc.

PubMed Search: Mastocytosis pathology [title]

Nikhil Sangle, M.D.
Page views in 2019: 998
Page views in 2020 to date: 329
Cite this page: Sangle N. Mastocytosis. website. Accessed April 7th, 2020.
Definition / general
  • Examine bone marrow with tryptase stain to confirm presence of abnormal (spindle shaped) mast cells, use flow cytometry of bone marrow to look for CD25+ (phenotypically abnormal) mast cells, mutation screening to find KIT D816V and to exclude other abnormalities (Haematologica 2008;93:6)

Diagnostic criteria:
  • Mastocytosis is working diagnosis if:
    1. bone marrow aggregates of morphologically abnormal mast cells are present or
    2. when histology is equivocal, if KIT D816V or phenotypically abnormal (CD25+) mast cells are present
  • Other requirements: no BCR–ABL, no dyserythropoiesis, no granulocyte dysplasia, no monocytosis, no rearrangements of PDGFRA, PDGFRB or FGFR1

Cutaneous mastocytosis:
  • Multifocal or diffuse infiltrates of morphologically abnormal or immunophenotypically clonal mast cells within the skin
  • Absence of features of systemic mastocytosis
  • Can have clinical findings of urticaria pigmentosa, diffuse cutaneous mastocytosis or solitary mastocytoma

Systemic mastocytosis (SM):
  • Major criteria and one minor OR three minor criterion

Major criteria:
  • Aggregates ( > 15 cells) of mast cells in bone marrow or extracutaneous organs

Minor criteria:
  • > 25% immature, spindled or atypical mast cells in bone marrow or extracutaneous organs
  • Presence of KIT D816V point mutation
  • Phenotypic expression of CD2 or CD25
  • > 20 ng/ml serum tryptase levels in the absence of clonal myeloid disorder

Various clinical patterns include:
  • Indolent SM (low mast cell burden with no skin lesions)
  • SM associated with clonal hematologic non mast cell lineage disease (MDS, MPN, AML or lymphoma)
  • Aggressive SM (meets criteria for SM, no evidence of mast cell leukemia or skin involvement)
  • Mast cell leukemia (mast cells > 20% of nucleated marrow cells, aleukemic if < 10% of WBC are mast cells)
  • Extracutaneous mastocytoma (unifocal mast cell tumor with nondestructive growth pattern)
  • Mast cell sarcoma (unifocal, destructive growth pattern with high grade cytological features)
Prognostic factors
  • Late onset of symptoms, absence of cutaneous involvement, elevated LDH, anemia, bone marrow hypercellularity, qualitative peripheral blood abnormalities, elevated alkaline phosphatase, and organomegaly
  • May not be necessary if indolent
  • IFN alpha and cladribine if systematic
  • Usually resistant to imatinib (since the D816V mutation causes ligand independent activation of KIT tyrosine kinase) (Curr Allergy Asthma Rep 2007;7:248)
Microscopic (histologic) description
  • Paratrabecular aggregates resembling microgranulomas of oval or spindled cells with clear cytoplasm and distinct cell outlines resembling hairy cell leukemia
  • Associated with eosinophils and thickened bone; focal lesions may be perivascular and associated with medial or adventitial hypertrophy and collagen fibrosis
Microscopic (histologic) images

Images hosted on other servers:

Bone marrow biopsy:

Various images

Chymase staining

Bone marrow smear:

Various images

With an associated clonal hematological non mast cell lineage disease

Positive stains
Negative stains
Molecular / cytogenetics description
Differential diagnosis
Back to top