Nucleophosmin (NPM1) mutations (NPM1mut) are present in approximately one-third of adults with acute myeloid leukemia (AML),1 and despite a generally favorable prognosis, a significant proportion (26%-44%) will relapse.2, 3, 4 Importantly, NPM1mut provides a stable target for monitoring measurable residual disease (MRD) using molecular methods,5 and patients with rising MRD levels after treatment (now called MRD relapse6) inevitably progress to frank relapse without intervention.7 The gene discussed is NPM1; the disease is acute myeloid leukemia.