Acute megakaryoblastic leukemia (M7 according to FAB classification) – diagnosis

Acute megakaryoblastic leukemia (M7 according to FAB classification):
• makes up 3-5% of all acute non-lymphoblastic leukemias (ONLL);
• in the bone marrow, the progenitors of the megakaryocyte series account for more than 50%;

• blasts are of two types:
1) with irregular outlines and pronounced basophilia of the cytoplasm, moderate nuclear-cytoplasmic ratio;
2) rounded with a high nuclear-cytoplasmic attitude, resembling lymphoblasts in appearance;

• in blasts, moderate activity of α-naphthylacetate esterase, resistant to sodium fluoride, and the absence of butyratesterase, is determined. In some cases, PAS-positive substance is located in the form of large clusters along the edge of the membrane against the background of diffuse staining of the cytoplasm;
• platelet peroxidase is determined by ultrastructural examination in the nuclear membrane and the endoplasmic reticulum of blasts;

• blasts express platelet antigens CD41 (glycoprotein IIb / IIIa) and / or CD61 (glycoprotein IIIa), less often CD42 (glycoprotein Ib), since the latter is expressed in more mature forms. For the diagnosis of M7 ONLL, it is necessary that the number of antigen-positive cells be more than 50%. CD13, CD33, CD36 are also detected;
• A variant of M7 leukemia in children with Down syndrome on the background of a transient myeloproliferative disease is separately highlighted. A number of patients may experience spontaneous remission.