Mastocytosis is a clonal (neoplastic) proliferation of mast cells. It can be a heterogeneous disorder ranging from skin lesion, which spontaneously regress, to aggressive systemic disease with a short survival. Mastocytosis is divided into two generalized categories: cutaneous mastocytosis (CM) and systemic mastocytosis (SM). CM is limited strictly to the skin, but SM has at least one extracutaneous organ involved (+/- skin involvement).
In SM the bone marrow is almost always involved. Approximately 50% of SM patients will have skin involvement.
Cutaneous Mastocytosis
- Diffuse Cutaneous Mastocytosis
- Mastocytoma of Skin
- Urticaria Pigmentosa (UP)/Maculopapular Cutaneous Mastocytosis (MPCM)
Systemic Mastocytosis
- Indolent Systemic Mastocytosis
- Systemic Mastocytosis with associated clonal hematological non-mast cell lineage disease (SM-AHNMD)
- Aggressive Systemic Mastocytosis (ASM)
- Mast Cell Leukemia
- Mast Cell Sarcoma
- Extracutaneous Mastocytoma
Immunohistochemistry
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Stain
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Comment
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CAE
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Strongly reactive (must be used in combination with MPO)
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MPO
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Negative
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Tryptase
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Positive, not specific. Positivity of spindle cells in the bone marrow (BM) is considered specific for mast cells. Positivity of round cells in the BM may represent one of three entities: (1) mast cells (CD117+, chymase +), (2) neoplastic basophils, or (3) AML.
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Chymase
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Subset Positive (highly specific but not sensitive)
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Positive
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Expressed in a subset of neoplastic mast cells (specific). Must differentiate from T-cells.
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Expressed in a subset of neoplastic mast cells (specific). Must differentiate from T-cells. Commonly expressed in neoplastic mast cells involving the GI tract.
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CD9
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Positive
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Positive
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Positive
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Positive
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Negative
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CD14
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Negative
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CD16
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Negative
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Reticulin
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In systemic mastocytsis with bone marrow involvement, there is often significant reticulin fibrosis.
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CAE – Naphthphol-ASD-Chloroacetate Esterase, MPO – Myeloperoxidase
Photomicrographs
References
Hematopathology. [edited by] Jaffe, ES. 1st. ed. Elsevier, Inc. © 2011.