Acute myelomonoblastic leukemia (M4 according to the FAB classification) – diagnosis

1) biclonal variant of acute myelomonoblastic leukemia:
• makes up 15-25% of all acute non-lymphoblastic leukemias (ONLL);
• blasts are represented by two types of cells – myeloblasts and monoblasts (biclonal variant);
• blasts express antigens CD33, CD13, CD14, CD15, react with MCA to peroxidase and lysozyme;
• llq23 or t (8; 21) anomaly can be detected;

2) bifenotypic variant of acute myelomonoblastic leukemia:
• makes up 1% of all acute non-lymphoblastic leukemias (ONLL);
• blasts are represented by a single cell type (bifenotypic variant);
• blasts are morphologically characterized as M2 myeloblasts;
• blasts contain peroxidase, lipids, granulocyte esterase and nonspecific esterase simultaneously suppressed by sodium fluoride in all cells;
• the immunophenotype of blasts is the same as that of cells in the biclonal variant;

3) myelomonoblastic with eosinophilia:
• M4eo accounts for about 10–12% of all acute non-lymphoblastic leukemia (ONLL);
• blasts are represented by two types of cells – myeloblasts and monoblasts;
• atypical eosinophils are present in the bone marrow, their number may exceed 6%. In eosinophilic myelocytes and metamyelocytes, large dark-colored granularity is detected;
• in blasts and eosinophils, inversion of chromosome 16 or t (l6; 16) is detected.

In accordance with the WHO classification, these observations are allocated to an independent category of acute non-lymphoblastic leukemia (ONLL) with recurring cytogenetic abnormalities.