Levels of the P-TEFb inhibitor hexamethylene bisacetamide-inducible protein 1 (HEXIM1) are upregulated during differentiation of murine leukemia cells [43], and HEXIM1 has been shown to be involved in the tumorigenesis of AML cell lines bearing the NPMc + mutation, the cytoplasmic-mislocated mutant form of NPM seen in approximately 35% of patients with AML [44]. The gene discussed is NPM1; the disease is acute myeloid leukemia.