Table of Contents
Definition / general | Case reports | Treatment | Gross images | Microscopic (histologic) description | Microscopic (histologic) images | Cytology description | Cytology images | Positive stains | Negative stains | Molecular / cytogenetics description | Differential diagnosisCite this page: Mihova D. Myeloid sarcoma. PathologyOutlines.com website. https://www.pathologyoutlines.com/topic/leukemiagranulocytic.html. Accessed March 7th, 2021.
Definition / general
- Extramedullary tumor mass of neoplastic immature myeloid (granulocytic or monocytic) cells
- Also called extramedullary myeloid tumor, granulocytic sarcoma, chloroma
- See also descriptions in various chapters
- Often misdiagnosed, particularly without immunostains
- Present in 2 - 8% of AML patients; prognosis is that of underlying leukemia
- Equivalent to blast transformation in setting of myelodysplastic syndrome or myeloproliferative disease (Korean J Lab Med 2006;26:143)
- Usually associated with AML M4 or M5 (M4e or M5a in children), CML, chronic idiopathic myelofibrosis, hypereosinophilic syndrome or polycythemia vera
- Rarely no leukemia / myelodysplasia is identified in blood or bone marrow (J Neurosurg 2006;105:916)
- Common sites: lymph nodes, subperiosteal bone, skin, orbit, spinal canal and mediastinum
Case reports
- 27 year old woman with punched out, lytic, intramedullary lesion in fibula (Case of the Week #130)
Treatment
- Aggressive treatment recommended (Leukemia 2007;21:340, Cancer 2002;94:1739)
- Usually evolves to AML or has additional tumor masses at other sites
Microscopic (histologic) description
- Blastic type: myeloblasts with mild / moderate rim of basophilic cytoplasm, fine nuclear chromatin, 2 - 4 nucleoli
- Immature type: myeloblasts, promyelocytes, eosinophilic myelocytes
- Differentiated type: promyelocytes, eosinophilic myelocytes and more mature forms; rarely crystalline inclusions similar to Charcot-Leyden crystals (Arch Pathol Lab Med 2002;126:85)
Microscopic (histologic) images
Cytology description
- Usually background lymphoglandular bodies
- Auer rods and eosinophilic myelocytes are rare
- Resembles large cell lymphoma (Cancer 2000;90:364)
Cytology images
Positive stains
- Almost all tumors: lysozyme and CD43
- Myeloid tumors: myeloperoxidase and CD117
- Myeloblasts: CD13, CD33 (Arch Pathol Lab Med 2001;125:1448)
- Monocytic tumors: CD68 and variable CD163 (Am J Clin Pathol 2004;122:794)
- Monoblasts: CD11c (Diagn Pathol 2007;2:42), CD14, CD56 (Am J Clin Pathol 2000;114:807), CD99 (55%, Mod Pathol 2000;13:452), HLA-DR and chloroacetate esterase (Ann Saudi Med 2001;21:287)
- Other: CD4, CD34 and TdT
Molecular / cytogenetics description
- Most common are monosomy 7 (11%), trisomy 8 (10%) and MLL rearrangements (9%)
- Also inv(16), trisomy 4, monosomy 16, 16q-, 5q-, 20q-, trisomy 11, t(8;21)(q22;q22) in pediatric cases and NPM1 mutations (16%)
Differential diagnosis
- Burkitt lymphoma
- Poorly differentiated lymphoma
- Small round cell tumors