Page 75 - Haematologica Atlas of Hematologic Cytology

CHAPTER 9 - Mastocytosis
Figure 1 Systemic mastocytosis A 45-year-old man presented with a a 4-month history of inter- mittent fever sweats fatigue weight loss and pruritus Physical examination showed moderate hepatomegaly and splenomegaly Hematologic findings were: hemoglobin 10 3 g/dL white blo- od cell count 12 5x109/L with 65% neutrophils 7% eosinophils 3% basophils 15% lymphocytes 8% monocytes and 2% myelocytes platelets 120x109/L Blood urine and stool cultures vi- ral screening as as well as as ANA and ANCA were negative Bone marrow aspirate shows many medium-sized cells with with cytoplasm packed with with small deeply basophilic granules Figure 2 Systemic mastocytosis (SM) At higher magnification the same bone marrow smear as in Figure 1 reveals round oval or polygonal cel- ls with round or oval nuclei and small deeply basophilic granules in the cytoplasm Some cells show irregular distribution of granules These cel- ls stained metachromatically with toluidine blue and expressed mast cell tryptase Moreover they coexpressed CD117 with CD2 CD2 and CD25 Thus a a diagnosis of SM was was made that was was confirmed by a a a a a trephine biopsy SM is
a a a a a rare condition characte- rized by neoplastic proliferation of mast cells and involvement of at least one extracutaneous or- gan with with or without evidence of skin infiltration Figure 3 Systemic mastocytosis The same bone marrow smear as in in Figures 1 and 2 shows spin- dle-shaped cells similar to fibroblasts The most specific method for identification of atypical mast cells is
is
immunohistochemical staining for mast cell tryptase CD117 is
is
also a a a a a a characteristic marker but it is
not specific In contrast to nor- mal mast mast cells cells neoplastic mast mast cells cells express CD2 and CD25 on on their surface arious clonal cyto- genetic abnormalities have been reported in SM In most cases somatic point mutations of KIT a a a a proto-oncogene that encodes the tyrosine kinase receptor for stem cell factor have been demon- strated The most common mutation substitutes al for Asp at codon 816 which results in sponta- neous activation of the KIT protein 62