Mastocytosis and related disorders

Urticaria pigmentosa in skin biopsy of an adult with clusters of dermal mast cells.

Systemic mastocytosis in bone marrow biopsy. The mast cell aggregate is sharply delineated and is present in the paratrabecular location (A). Within the mast cell lesion are many spindle-shape mast cells with admixed eosinophils, fibroblasts, and small lymphocytes (B).

The mast cells lesions typically show significant fibrosis with the presence of collagen, as shown by reticulin (A) and collagen (B) histochemical stains. In contrast with other fibrogenic myeloid neoplasms, the mast cell lesions are poor in vascularity as demonstrated by CD34 immunostaining (C). There is significant thickening (osteosclerosis) of the adjacent trabecular bone (D).

The neoplastic mast cells are often spindled shaped with asymmetric distribution of cytoplasmic metachromatic granules (A), although a variable number of round forms is usually also identified (B). Frequent atypical bi- or multilobated forms are seen in this case (C).

A case of primary myelofibrosis (cellular phase) with positive JAK-2 V617F point mutation marked by the presence of atypical, hyperlobated megakaryocytes forming clusters (A). The adjacent marrow shows an aggregate of mast cells (B) highlighted by mast cell tryptase immunostaining (C), indicating involvement by systemic mastocytosis with associated clonal hematological non mast cell lineage disease (SM-AHNMD/SM-PMF).

A case of mast cell leukemia showing a markedly increased number of atypical mast cells in the bone marrow aspirate smear (A) and peripheral blood involvement (B). The bone marrow biopsy shows diffuse infiltration by the neoplastic mast cells (C) that are highlighted by mast cell tryptase immunostain (D).

Immunohistochemistry in a case of systemic mastocytosis. The mast cells are positive for mast cell tryptase (A) and CD117 (KIT) (B) and show aberrant expression for CD25 (C) and CD2 (D).

A case of FIP1L1–PDGFRA rearranged chronic eosinophilic leukemia. Note the increased number of mast cells (A), highlighted by mast cell tryptase (B).