myeloid sarcoma (extramedullary myeloid tumor, granulocytic sarcoma, chloroma)

Pathology

• solid tumor of myeloblasts or immature myeloid cells in an extramedullary site or in bone
• granulocytic form also contains neutrophils
• less common monoblastic form
• tumors of 3 lineages: myeloblasts, erythroblasts & megakaryocytes

Genetics

• chromosomal translocation: t(8;21)(q22;q22)
• chromosomal inversion: inv(16)(p13q22)
• chromosomal translocation: t(16;16)(p13;q22)
• monoblastic form: translocations involving 11q23

Clinical manifestations

• may precede or occur concurrently with:
  • acute myeloid leukemia (AML)
  • chronic myeloid leukemia
  • myelodysplastic syndrome
  • other myeloproliferative disorders
• may be interval of months to years between occurrence of myeloid sarcoma & AML
• may be initial manifestation of relapse in previously treated AML in remission
• sites of occurrence
  • subperiosteal bone of skull, paranasal sinuses, sternum, ribs, vertebrae, pelvis
  • lymph nodes
  • skin

Laboratory

• immunophenotyping by flow cytometry or immunohistochemistry
  • myelomonocytic antigens
  • myeloperoxidase
  • chloroacetate esterase
• expression of myeloid-associated antigens
  • CD13
  • CD33
  • CD117
  • CD43 (most)
• monoblastic form may express
  • CD14
  • CD116
  • CD11c
  • CD68 (generally)
• CD61 NOT expressed (used to rule out myeloid sarcoma)

Differential diagnosis

• non Hodgkin's lymphoma, lymphoblastic type
• Burkitt lymphoma
• large cell lymphoma
• small round cell tumors, especially in children
  • neuroblastoma
  • rhabdomyosarcoma
  • Ewing's sarcoma
  • medulloblastoma

Management

• when occurring concurrently with leukemia, prognosis is that of underlying leukemia
• as an isolated lesion, radiation therapy may be curative

More general terms

• sarcoma
• myeloproliferative disorder
• hematologic malignancy