Heterogeneous leukemic clones identified by NPM1 mutation analysis in patient with acute monocytic leukemia

NPM1 mutation is the most common molecular abnormality in patients with acute myeloid leukemia (AML), especially normal karyotype AML (NK-AML), and is associated with a favorable prognosis in the absence of concomitant FLT3-ITD. Like other molecular abnormalities such as FLT3-ITD, C/EBPα and c-Kit mutation, NPM1 mutation normally presents as a recurrent molecular abnormality. The NPM1 mutation is generally used as a molecular marker in the prognosis evaluation of a patient with AML. Here, we report a different case. He was first diagnosed with NPM1 mutation-positive acute monocytic leukemia. However, he achieved no remission, but the NPM1 mutation dramatically became negative after induction chemotherapy. Finally, he achieved complete remission after salvage chemotherapy and the NPM1 mutation was still negative. To our knowledge, this is a rare case according to the worldwide published literature.