University of Virginia Health System

Acute Myeloblastic Leukemia Without Differentiation
(M1 AML)

M1 acute leukemia- Bone marrow aspirate smear, Wright-Giemsa stain, 1000x

Description:

This subtype accounts for up to 20% of AML in adults.

The blasts vary in size, but are approximately the size of mature segmented neutrophils. The nuclei are round to slightly oval or irregular, and the nuclear chromatin ranges from finely granular and evenly distributed to slightly clumped. One to two nucleoli are usually visible. The cytoplasm is scant and grey-blue to light blue in color, and agranular. The nuclear:cytoplasmic ratio is high. Auer rods are seen in a minority of blasts. By morphology alone, M1 blasts cannot be distinguished from M0, agranular M2 blasts or L2 blasts. Minimal differentiation is seen, and usually is manifested by scattered normal promyelocytes or more mature, normal neutrophilic cells. In this setting, if Auer rods are seen, as in the example above, the diagnosis of M1 AML is established. 

Cytochemistry:

The blasts are positive for myeloperoxidase (MPO) and Sudan black B, but negative for non-specific esterase (NSE).

Immunophenotype:

• Stem cell and early hematopoietic progenitor markers: CD34+, HLA-DR+, Tdt+
• Myeloid lineage markers: CD117+, CD13+, CD33+, MPO+

Prognosis:

Response to induction chemotherapy and response duration are quite variable, and depend on many other factors e.g. age of patient, cytogenetics, whether de novo or emerging from a myelodysplastic or myeloproliferative disorder, or after exposure to certain drugs or toxins (secondary leukemia).

General References:

• Bennett JM, Catovsky D, Daniel MT, et al: Proposed revised criteria for the classification of acute myeloid leukemia: A report of the French-American-British Cooperative Group. Am Intern Med 103:620, 1985
• Jaffe ES, Harris NL, Stein H, Vardiman JW, eds. Pathology and genetics of tumors of hematopoietic and lymphoid tissues. Vol. 3 of World Health Organization classification of tumors, Lyon, France: IARC Press, 2001

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