Mast Cell Disease (Mastocytosis)

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
Stain
Comment
CAE
Strongly reactive (must be used in combination with MPO)
MPO
Negative
Tryptase
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.
Chymase
Subset Positive (highly specific but not sensitive)
Positive
Expressed in a subset of neoplastic mast cells (specific).  Must differentiate from T-cells.
Expressed in a subset of neoplastic mast cells (specific).  Must differentiate from T-cells.  Commonly expressed in neoplastic mast cells involving the GI tract.
CD9
Positive
Positive
Positive
Positive
Negative
CD14
Negative
CD16
Negative
Reticulin
In systemic mastocytsis with bone marrow involvement, there is often significant reticulin fibrosis.
CAE – Naphthphol-ASD-Chloroacetate Esterase, MPO – Myeloperoxidase
Photomicrographs
Systemic Mastocytosis - CD117
Systemic Mastocytosis – CD117
Systemic Mastocytosis - H&E
Systemic Mastocytosis – H&E
References
Hematopathology. [edited by] Jaffe, ES. 1st. ed. Elsevier, Inc. © 2011.