IHC in NPM1-mutated AML and myeloid sarcoma.NPM1-mutated AML with multilineage dysplasia showing infiltration by blasts (double arrows) and a monolobated megakaryocyte (single arrow) (bone marrow biopsy, immune-alkaline phosphatase staining, original magnification ×400) (top left panel). Reprinted from Pasqualucci et al.⁷⁷  Another case of NPM1-mutated AML with multilineage dysplasia double stained for NPM1 (blue) and GATA1 (brown) (top right panel). Numerous erythroid leukemic cells (GATA1 nuclear brown/NPM1 cytoplasmic blue) are present. The arrow indicates a residual normal erythroid cell (original magnification ×400; double staining with immune-alkaline phosphatase/immunoperoxidase). Skin biopsy, showing dermal infiltration by leukemic cells (original magnification ×400; hematoxylin and eosin stain) (middle left panel). Leukemic cells from the same patient show aberrant cytoplasmic expression of NPM1, confirming the diagnosis of NPM1-mutated skin myeloid sarcoma (middle right panel). Normal cells of the overlying epidermis show nucleus-restricted expression of NPM1 (arrow) (original magnification ×400; immune-alkaline phosphatase staining). Testicular biopsy showing massive infiltration by leukemic cells and a residual seminiferous tubule (*) (original magnification ×400; hematoxylin and eosin stain) (bottom left panel). Leukemic cells from the same patient show aberrant cytoplasmic expression of NPM1, confirming a diagnosis of testicular myeloid sarcoma (bottom right panel). Cells of a normal residual seminiferous tubule (*) show nuclear expression of NPM1 (arrow) (original magnification ×400; immune-alkaline phosphatase staining). E, epidermis.