NPM1 and acute myeloid leukemia: Nucleophosmin, nucleolar phosphoprotein B23, located within the nucleolus, is a nucleocytoplasmic shuttling protein involved in chaperoning ribosomal proteins and core histones from the nucleus to the cytoplasm as well as regulating the ARF-p53 tumor suppressor pathway.5 Mutations in the nucleophosmin (NPM1) gene are the most frequently occurring gene mutations in AML.6 These mutations identify patients that respond better to chemotherapy and have improved outcomes.7