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CD34 immunostain typically highlights the interspersed mononuclear cells that vary in size from small to medium in the bone marrow biopsy and correspond to either blasts or hematogones. Background shows negative staining in erythroid, lymphoid and mature myeloid cells. Note numerous dysplastic megakaryocytes in this image staining with CD34 (black arrows). Frequently such aberrant staining may be seen in malignant myeloid processes including cases with inversion (3) AML. 

 Blasts in this entity express myeloid antigens such as CD33, CD13 and CD117 with frequent aberrant expression of CD7 by flow cytometry. Multilineage dysplasia, typically with increased number of dysplastic, small, non-lobated megakaryocytes is clue to the diagnosis as noted here. This is an aggressive disease and cases with <20% blasts are not currently classified as AML but can be treated as such if clinically appropriate.