University of Virginia Health System

Acute Myeloblastic Leukemia With Minimal Differentiation
(M0 AML)

M0 acute leukemia- Bone marrow aspirate smear, Wright-Giemsa stain, 1000x

Description

This subset represents <5% of AMLs in adults.

Even though this subtype is described as having minimal differentiation, from a morphologic standpoint, there is little to no evidence of maturation. The blasts are approximately the size of a normal mature segmented neutrophil, although the size varies; the larger blasts probably represent those near the end of the S phase of the cell cycle. The cytoplasm is usually scant, and grey to light blue in color without granules, and Auer rods are not seen. The nuclear:cytoplasmic ratio is high. The nucleus is round to oval or irregular and usually eccentrically placed. The nuclear chromatin ranges from being finely granular and evenly dispersed to being slightly clumped. One or more nucleoli may be visible. There is minimal to no differentiation along the myeloid line that can be detected by light microscopy. By morphology alone, the blasts cannot be distinguished from those seen in M1 AML, the agranular blasts in M2 AML, and those seen in L2 ALL.

Cytochemistry

The blasts are myeloperoxidase (MPO), Sudan black B, and nonspecific esterase negative.

Immunophenotype

• Stem cell and hematopoietic progenitor cell markers: CD34+, HLA-DR+, and TdT+
• Myeloid lineage markers: CD117+, CD13+ and CD33+. Note that the cytochemistry stain for MPO is usually negative, but positive by immunophenotyping.
• T cell markers: CD7 is frequently positive, and is an example of what has been designated bilineage, biphenotypic, mixed lineage, or hybrid acute leukemias.

Cytogenetics

Although no signature abnormality has been identified, complex karyotypes and abnormalities of chromosomes 5, 7, and 11 are relatively common.

Prognosis

Very poor, especially if associated with bad cytogenetics.

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
• Vallamor N, Zorco MA, Rogman M, et al: Acute myeloblastic leukemia with minimal differentiation: Phenotypical and ultrastructural characteristics. Leukemia 12:1071, 1998 

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