Nucleophosmin (NPM1) is a nuclear phosphoprotein that shuttles between the nucleolus and cytoplasm, and is involved in proliferation and growth-suppression pathways. It is involved in ribosome biogenesis, regulates centrosome duplication, and is involved in regulation of the ARF/p53 pathway. Overexpression correlates with cell transformation, and disruption can cause genomic instability and centrosome amplification. When mutated, NPM1 is trapped in the cytoplasm, and the aberrant cytoplasmic location has been used to identify NPM1 mutation status in AML patients. Translocations and fusions with several genes (ALK, RARalpha, MLF1) have been identified in various lymphomas and leukemias. References: Nat Reviews Cancer 2006 6:493; Ind J Med Res 2016 143(6):763; Heamatologica 2013 98(10):1532; Haematologica 2007 92(4):519