Hematogenous neoplasms

Topic Completed: 1 April 2013

Minor changes: 1 April 2020

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PubMed Search: Mastocytosis[TI] spleen

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Cite this page: Mansouri J. Mastocytosis. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/spleenmastocytosis.html. Accessed May 29th, 2020.
Definition / general
  • Considered a myeloproliferative disorder
  • Spleen not involved in indolent systemic mastocytosis but splenomegaly is present in 72% with systemic mastocytosis; may involve splenic hilar lymph nodes with perifollicular and perivascular involvement
WHO classification
  • Indolent systemic mastocytosis
    • Provisional subvariants: isolated bone marrow mastocytosis, smoldering systemic mastocytosis
  • Systemic mastocytosis (SM) with hematopoietic clonal nonmast lineage disease (Hematol Oncol Clin North Am 2012;26:1117)
    • Provisional subvariants: SM - acute myeloid leukemia; SM - myelodysplastic syndrome; SM - myeloproliferative disorder; SM - chronic myeloid leukemia; SM - chronic myelomonocytic leukemia; SM - non-Hodgkin lymphoma
  • Aggressive systemic mastocytosis
    • Provisional subvariant: lymphoadenopathic mastocytosis with eosinophilia
  • Mast cell leukemia (Am J Hematol 2012;87:401)
  • Diagnostic criteria: one major and one minor OR three minor criteria
  • Major criterion: multifocal dense infiltrates of mast cells (> 15 mast cells in aggregates) in bone marrow biopsies or sections of other extracutaneous organ(s)
  • Minor criteria:
    1. Greater than 25% of all mast cells are atypical in bone marrow smears or are spindle shaped in mast cell infiltrates detected on sections of visceral organs
    2. CD117 (c-kit) point mutation at codon 816 in the bone marrow or another extracutaneous organ
    3. Mast cells in bone marrow, blood or other extracutaneous organ express CD2 or CD25
    4. Baseline serum tryptase concentration > 20 ng/ml (in the case of an unrelated myeloid neoplasm, (D) is not valid as an SM criterion)
  • Elevated serum tryptase levels (not for cutaneous mastocytosis), proportional to mast cell infiltration of bone marrow; may also be elevated for other myeloid neoplasms
Case reports
Gross description
  • Enlarged spleen with ill defined granulomas with fibrotic appearance scattered throughout spleen
Microscopic (histologic) description
  • Highly fibrotic foci centered on blood vessels in red and white pulp
  • Small clusters of mast cells embedded in fibrous tissue, with variable eosinophils, lymphocytes, histiocytes
  • Mast cells in systemic mastocytosis often have atypia, including spindle shapes, hypogranulated cytoplasm, oval decentralized nuclei, multiple nuclear lobes or myeloblasts type cells
Microscopic (histologic) images

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Mast cell leukemia

Bone marrow biopsy

Positive stains
Negative stains
Molecular / cytogenetics description
Differential diagnosis
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