Influence of Nucleophosmin ( NPM1 ) Genotypes on Outcome of Patients With AML: An AIEOP-BFM and COG-SWOG Intergroup Collaboration

PURPOSE Several genomic subsets of NPM1 mutations with varying sequences (type A, B, D, etc) have been identified. Despite molecular heterogeneity, NPM1 mutations cumulatively portend a more favorable outcome, but biology and prognostic implications of different genomic subsets have not been extensively studied. In this multicentric study, we investigated the impact of NPM1 genotypes on patient's outcomes and interrogated the underlying biology of the different subtypes. MATERIALS AND METHODS Of more than 4,000 patients enrolled in multiple pediatric cooperative (AIEOP, BFM, ELAM02, NOPHO, DCOG, and COG trials), or adult (SWOG) trials, 348 pediatric and 75 adult AML patients with known NPM1 genotype and available outcome were selected for this study. Diverse NPM1 variants were correlated with the probabilities of overall survival (OS) and event-free survival. Nuclear localization and translational efficiency of the NPM1 variants was studied. RESULTS Evaluation of clinical outcome on the basis of NPM1 genotypes showed that patients with type A, B, and other rare variants had similarly favorable outcomes, whereas those with type D had a significantly worse outcome (OS of 63% for type D v 86% for type non-D, P = .005). Multivariate analysis confirmed type D as an independent prognostic factor associated with inferior OS (hazard ratio, 3; P = .005). In vitro, we demonstrated that in type D versus type A synonymous variants, codon optimality plays major roles in determining gene expression levels, and translation efficiency, which resulted in a more expressed NPM1-D mRNA and protein, mediating peculiar mitochondrial gene expression. CONCLUSION The evaluation of specific NPM1 genotypes identified AML patients with type D mutations being significantly associated with inferior outcomes, suggesting a reclassification of D cases to higher-risk groups.