Starry sky pattern predicts RAS pathway activation in NPM1‐mutated acute myeloid leukemia

Abstract

I M A G E 1 NPM1-mutated AML with starry sky pattern (Case 3). (A) Diffuse bone marrow infiltration by leukemic cells; many tingible body macrophages (arrow) imparting a starry sky pattern are seen (bone marrow biopsy, hematoxylin-eosin, Â400). (B) Tingible body macrophages are positive for macrophage-restricted CD68 (bone marrow biopsy; immune-alkaline phosphatase APAAP staining, Â400). (C) Leukemic cells express myeloperoxidase (MPO) (bone marrow biopsy; immune-alkaline phosphatase APAAP staining, Â400). (D) Leukemic cells show cytoplasmic expression of NPM1 in leukemic cells while the tingible body macrophages are negative (arrow; bone marrow biopsy; immunostaining with monoclonal antibody specific for NPM1 mutant A (NPM1c); immunoperoxidase; Â400).