A promonocyte (arrow) is strongly positive for alkaline phosphatase (ALP) activity (blue cytoplasmic granules) in a dog with acute myelomonocytic leukemia (confirmed by morphologic features, bone marrow aspirates revealing >20% myeloid blasts, additional cytochemical stains, and flow cytometric analysis). The three other cells in the image are neutrophil progenitors, which are negative for ALP. The latter cells were positive for chloroacetate esterase (CAE) on cytochemical staining (not shown), confirming their neutrophil lineage.
