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Systemic mastocytosis
Bone Marrow, Iliac Crest
Haematoxylin & Eosin (H&E)
44 years
44-year old male patient with cutaneous mastocytosis. Clinicians asked for bone marrow manifestations of the disease in terms of a systemic mastocytosis.
Core biopsy cylinder of a normocellular (ca. 50%) bone marrow. Megakaryopoiesis is irregularly distributed but cytologically inconspicuous. Erythropoiesis is slightly disorganized but free of dysplasia. Myelopoiesis is regularly maturing. The peritrabecular and perivesicular space is infiltrated by compact aggregates of mast cells resembling fibrohistiocytic lesions. Mast cells excel through an atypical morphology appearing spindled and hypogranular with prominent nucleoli. Aggregates are associated with eosinophils and lymphocytes.
Immunophenotyping confirmed mast cell origin by identifying a coexpression of CD117 and tryptase. Molecular genetics were performed and gene-sequencing proved a sequence-alteration (p.D816V) in exon 17 of the CKIT-gene. The mutation is most commonly found (>90%) in cases of systemic mastocytosis and linked to a resistance to Imatinib. Giemsa staining revealed clusters (>15 cells) of mast cells.
Systemic mastocytosis is diagnosed when one major [clusters (>15 cells) of mast cells] and one minor criterion or three minor criteria are met. Minor criteria: I: More than 25% of mast cells in the infiltrate have atypical morphology (in biopsy section) or all mast cells have atypical morphology (in aspirate smear). II Mast cells co-express CD117 with CD2 or CD25. III Detection of KIT point mutation at codon 816 in bone marrow, blood or other extracutaneous organs. IV Serum total tryptase levels are persistently over 20ng/ml.
Kaya Veelken, University of Basel
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