Proposal for the recognition of minimally differentiated acute myeloid leukaemia (AML‐MO)

Abstract

We describe a form of acute myeloid leukaemia (AML), designated AML-MO, with minimal myeloid differentiation, not included previously in the FAB classification. AML-MO cannot be diagnosed on morphological grounds alone as the blast cells are large and agranular, sometimes resembling L2 or, rarely, L1 lymphoblasts, and should be identified by the following features: negative myeloperoxidase (MPO) and Sudan Black B reaction (or positive in less than 3% of blasts), negative B and T lineage markers and expression of myeloid antigens recognized by at least one monoclonal antibody, CD13 or CD33. Other myeloid markers are also often positive and these include CD11b and the enzyme MPO demonstrated by immunocytochemistry and/or electron microscopy analysis. The findings in a group of 10 cases satisfying the criteria for AML-MO are described. AML-MO represents 2-3% of all cases of AML and 1-1.5% of all acute leukaemias. Its clinical and biological significance is not yet apparent but its identification in a larger number of cases may achieve this aim.

Immunophenotyping of Acute Leukaemias : A Critical Analysis of 35 Cases

“…The ultrastructural detection of MPO in blast cells is a valuable tool as a sensitive and specific marker for myeloid cells [21]. The FAB group suggests that demonstration of MPO positive blasts by transmission electron microscopy or reactivity with CD 13 or CD 33 is sufficient for diagnosing AML MO [22].…”

Myeloid Sarcoma: Presenting with Massive Cervical and Inguinal Lymphadenopathy

“…The French-American-British Cooperative Group (FAB) described 8 AML subtypes based originally on morphologic and cytochemical features. Other studies, including immunophenotype and, in some cases, electron microscopy were later added defining features of some subtypes [2][3][4]. Although the terminology of the FAB classification continues to be used by pathologists/hematopathologists, the system is now considered obsolete A complex approach is necessary for appropriate diagnosis and classification of AML or MS.…”

True

“…We analyzed nine patients with AML-M0, 23 patients with more differentiated AMLs, and three patients with non-hematopoietic cancers (for the analysis of granulocyte colony-stimulating factor (G-CSF)-mobilized hematopoietic progenitors). Diagnosis was established following FAB classification 1 and specific recommendations for AML-M0 distinction: 2,3,10,20 (1) negativity of light microscopy myeloperoxidase and Sudan black-B or positivity in less than 3% of blasts; (2) negative lymphoid markers (positive terminal deoxynucleotydil transferase or CD7 were accepted); (3) positive CD13 and/or CD33. Slides were independently reviewed by two morphologists (DS and CA).…”