(A) May-Grunwald-Giemsa stained cytospin of APL microgranular variant (Table 3, case 10). Notice the blast cells with markedly lobulated and invaginated nuclei (double arrows). The cytoplasm of APL cells contains no clearly recognizable granules (original magnification × 800). The single arrows indicate normal lymphoid elements. (B) Immunolabeling of the same case with the PG-M3 MoAb shows a microgranular distribution of the PML/RARα protein within the nuclei of APL cells (double arrows). This pattern contrasts with the nuclear speckled positivity (PML wild-type) of normal residual hemopoietic elements (single arrows) (indirect immunofluorescence with rhodamine-labeled antibody; nuclear DAPI counterstain; original magnification × 1,000). (C) Acute nonlymphoid leukemia of M4 subtype. Notice the typical speckled positivity (PML wild type) of blast cells (indirect immunofluorescence with fluorescein-labeled antibody; nuclear DAPI counterstain; original magnification × 1,000). (D) Peripheral blood smear of APL microgranular variant (Table 3, case 11) showing hypogranulated blasts with marked nuclear folding (arrow) (May-Grunwald-Giemsa; original magnification × 800). (E and F) The nuclei of APL cells from the same case as Fig 1D show the typical micropunctate positivity of the PML/RARα fusion protein (APAAP technique; hematoxylin counterstain; original magnifications: [E] × 800; [F ] × 1,000). (G) Acute nonlymphoid leukemia of M5 subtype. The leukemic cells display the typical speckled positivity of wild-type PML (APAAP technique; hematoxylin counterstain; original magnification × 1,000).