Acute monoblastic leukemia (M5a according to FAB classification) – diagnostics

Acute monoblastic leukemia without maturation (M5a according to FAB classification):
• accounts for 5–8% of all acute non-lymphoblastic leukemias (ONLL);
• blasts of large size, irregular outlines, with moderate or severe cytoplasmic basophilia, with rounded nuclei with 1-2 nucleols; in rare cases, erythrophagocytosis is observed;
• blasts contain a significant amount of nonspecific esterase suppressed by sodium fluoride, a small amount of peroxidase and / or lipids in individual cells;
• blasts express the myeloid antigens CD33, CD13, CD117 and monocytic – CD14, as well as CD4, CDllb, CDllc, CD64, CD36, react with MCA to lysozyme;
• translocations (9; 11), (11; 19), (4; 11) are often detected with the participation of the MLL gene localized at llq23. In accordance with the WHO classification, these observations are categorized as the acute non-lymphoblastic leukemia category with recurring cytogenetic abnormalities.

Acute monoblastic leukemia with maturation (M5b according to the FAB classification):

• makes up 3-6% of all acute non-lymphoblastic leukemias (ONLL);
• more than 20% of blasts have a characteristic monocytoid form of the nuclei, a weakly basophilic cytoplasm with a small granularity and vacuolization;
• blasts contain a significant amount of nonspecific esterase suppressed by sodium fluoride, a small amount of peroxidase and / or lipids in individual cells;
• blasts express the antigens CD33, CD13, CD14, CD15 and react with the ICA to lysozyme;
• t (9; ll), t (ll; 19), t (4; ll) are often detected with the formation of the MLL gene localized at llq23. In accordance with the WHO classification, these observations are categorized into an independent category of acute non-lymphoblastic leukemia (ONLL) with recurring anomalies.