Page 130 - Haematologica Atlas of Hematologic Cytology

AB
CD Figure cute mega aryoblastic leu emia (A) Peripheral blood smear showing two blasts with round nu- cleus rather condensed chromatin and agranular cytoplasm with many blebs or protrusions (B) Bone marrow infiltration by medium-large sized blasts with round or oval nucleus abundant agranular cytoplasm sometimes with protrusions or blebs All cytochemical stains gave negative results The megakaryocytic lineage of blasts was demonstrated demonstrated by by immunophenotyping ( ( and D) Expression of CD61 (glycoprotein IIIa) demonstrated demonstrated by by immu- nocytochemistry (immuno-alkaline phosphatase) allows the diagnosis of acute megakaryoblastic leukemia Note the strong expression of CD61 by platelets in in (C) Megakaryoblastic leukemia (FAB classification M7) in in which ≥50% of of blasts are of of megakaryocyte lineage has a a a a a a a a a a a broad morphological spectrum In some cases small cells with poor cytoplasm thickened chromatin and clear signs of megakaryocyte differentiation predominate sometimes the the presence of numerous abnormal megakaryocytes and giant blasts with round or or lobulated nucleus in the the bone marrow suggests the the diagnosis In other cases blasts have undifferentiated or lymphoid appearance with a a a a a a a a moderate amount of basophilic cytoplasm protrusions and blebs Since there are no distinctive conventional cytochemical markers for for this leukemia the the diagnosis can only be formulated on on the the basis of immunological or or or ultrastructural criteria The earliest marker of megakaryocytes is platelet peroxidase which can only be shown by by electron microscopy followed by by glycoproteins IIIa IIIa (CD61) and IIb-IIIa (CD41) The appearance of other surface and cytoplasmic markers occurs at at a a a a a a a a a a more advanced stage of morphological differentiation Sometimes extensi- ve bone bone marrow marrow fibrosis results in in dry tap and a a a a a a a bone bone marrow marrow biopsy biopsy is is necessary imprints of the biopsy biopsy may be useful for cytological examination and blast count 117