Clinical implications of minimal residual disease monitoring by quantitative polymerase chain reaction in acute myeloid leukemia patients bearing nucleophosmin (NPM1) mutations

To explore the validity and prognostic significance of minimal residual disease detection by quantitative polymerase chain reaction (qPCR) in patients of acute myeloid leukemia (AML) bearing Nucleophosmin (NPM1) mutations, we quantified mutants in 194 bone marrow samples from 38 patients with a median follow-up time of 20.6 months. Following induction chemotherapy, a median of 2.78 log decline in mutant copy number was observed. Relapse was always accompanied by significant increase of mutant numbers (P<0.001). After achieving complete remission (CR), the mutant copy number was significantly higher in patients with subsequent relapse than in those remaining in continuous CR (P<0.001). Presence of detectable mutants after treatment predicted relapse if no further chemotherapy was administered. Furthermore, the patients with any rise of mutant signals during serial follow-up had 3.2-fold increase of relapse risk compared to those with persistently low or undetectable signals (P<0.001). Patients who could achieve mutant reduction to <0.1% of internal control had significantly longer overall survival (OS) (P=0.004) and relapse-free survival (RFS) (P<0.001). Failure to achieve 2 logs of reduction after consolidation predicted shorter OS (P=0.01) and RFS (P=0.001). In conclusion, qPCR monitoring may have prognostic impact in AML patients with NPM1 mutations.