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Leukemia - Acute

AML not otherwise categorized

Myeloid sarcoma

Reviewer: Daniela Mihova, M.D. (see Reviewers page)
Revised: 20 March 2013, last major update September 2012
Copyright: (c) 2001-2013, PathologyOutlines.com, Inc.


● 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)


● Aggressive treatment recommended (Leukemia 2007;21:340, Cancer 2002;94:1739)
● Usually evolves to AML or has additional tumor masses at other sites

Gross images

Kidney tumor   Bone tumor

Micro 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)

Micro images

Differentiated (left) versus blastic       Various images
types (center and right)-site unknown

Lymph node:
Cells have fine chromatin resembling     Large blast cells resemble large cell lymphoma,
lymphoblastic lymphoma          also some eosinophilic myelocytes

Tumor cells have irregularly        Resembles lymphoblastic lymphoma,
folded and convoluted nuclei        but has cytoplasmic granules and distinct nuclei

Many tumor cells have azurophilic     Tumor cells mix with residual normal lymphocytes

Immature cells with moderate to abundant cytoplasm,
round / oval nuclei, distinct and prominent nucleoli and immature eosinophils

Lymph node has prominent eosinophilic myelocytes and blasts

Case of the week #130 (bone):
                                       CD45 / LCA

CD45RO      CD3        CD34       CD20


Anorectal ulcer


Breast                 Has blasts with numerous azurophilic granules
                    and promyelocytes, classified as AML with maturation

Bladder       Skin-eosinophilic myelocytes and blasts

Small intestine

Orbital mass with t(8;21) has blasts with immature eosinophils

Soft tissue of paracervical        Spinal dura-some tumor cells
spine (H&E and CD99)          have cytoplasmic granules


Myeloperoxidase: Lymph node     Mediastinum   Breast (left), CD43 (right)

Skin: various stains

CD68: Spine    Uterus

Chloroacetate esterase - lymph node     Lysozyme - orbit

Cytology description

● Usually background lymphoglandular bodies
● Auer rods and eosinophilic myelocytes are rare
● Resembles large cell lymphoma (Cancer 2000;90:364)

Cytology images

Breast: has blasts with numerous azurophilic granules and promyelocytes, classified as AML with maturation

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

Negative stains

● CD3, CD20, CD34 and CD79a

Molecular 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

Myeloid sarcoma of female genital tract

● Rare, but may be initial clinical presentation
● Usually ovary, also vagina and cervix (Am J Surg Pathol 1997;21:1156, Am J Clin Pathol 2006;125:783)
● Mean age 40 years, range 13-76 years
Enzyme cytochemistry: chloroacetate esterase, lysozyme, myeloperoxidase, CD43, CD68, CD117

Micro description

● Usually diffuse growth pattern, also cords and pseudoacinar spaces; sclerosis common

Micro images

Left to right: Pelvic mass (various images), uterus (various images)

Differential diagnosis

● Carcinoma
● Granulosa cell tumor
● Lymphoma

End of Leukemia - Acute > AML not otherwise categorized > Myeloid sarcoma

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