This was from a practice teaching case and I'm not sure I agree...Hypercellular bone marrow with 94% blasts; no Auer rods identified. Blast immunophenotype: CD45 dim to negative, CD34+, CD117-, HLA DR+, TdT-/+ (minor subset positive), MPO-,surface CD3-, ic CD3-, CD19-, ic CD79a-, CD20-, CD10-, CD13+,CD33+/- (partial), CD11b-, CD14-, CD64-, CD56-, CD4+/-, CD8-, CD2-, CD5-, CD7-/+(minor partial), CD38+, CD41-, CD62-,GlyA favor-, CD71 favor- Immunohistochemistry confirmed flow findings. Cytogenetics are normal. FLT3, NPM1, CEBPA are negative. In the absence of cytochemistry results for MPO or butyrate esterase (which no one really does these days), would you still call this AML MO (WHO designation AML, NOS)? On page 150 of the WHO 2008, there is a table indicating that assignment of myeloid lineage requires MPO positivity. There is also the entity on page 151, "Acute undifferentiated leukemia".