Morphologic and cytochemical features of myeloid/NK cell precursor acute leukemia. MG-stained bone marrow smear of patients no. 4 (A) and no. 3 (B). (A) The leukemic cells show a L2-shaped morphology, with varying cell size, irregular nuclei with prominent nucleoli, and pale cytoplasm. Azurophilic granules are not apparent in the cytoplasm (original magnification × 1,200). (B) The leukemic cells present with unremarkable nucleoli and some with deeply invaginated nuclear membrane (original magnification × 1,200). (C) MPO-stained bone marrow smear of patient no. 3. Less than 3% of leukemic cells are positive for MPO staining (original magnification × 1,200).