The Detection of Multilineage Dysplasia (MLD) Has No Influence on Prognosis in NPM1 Mutated Acute Myeloid Leukemia (AML) with Normal Karyotype
Authors: Bacher Ulrike , Schnittger Susanne , Kern Wolfgang , Weiss Tamara , Haferlach Claudia , Falini Brunangelo , Haferlach Torsten 
Published: April 2020

Abstract
Acute myeloid leukemia with mutated nucleophosmin (AML NPM1mut) represents about one-third of all adult AML and shows distinctive biological and clinical features. For this reason, AML NPM1mut is planned to be included as a separate category in the revised WHO classification. A yet controversial issue, however, is whether AML NPM1mut with or without multilineage dysplasia (MLD) may differ biologically and clinically, as the presence of MLD might confer a negative prognostic impact. A further feature that was suggested to be typical for NPM1 mutated AML is “cup-like” morphology of blasts. We here analyzed 128 pts with AML NPM1mut and normal karyotype at first manifestation (59 females, 69 males; median age 60.5 years; 23.5–79.3 y). We investigated in parallel cytomorphology from bone marrow and/or peripheral blood, chromosome banding analysis, and molecular analyses. Presence of dysplasia was defined by dysplastic features in ≥50% of cells in the respective hematopoietic lineage as defined by the WHO. A 5% cut-off was taken for the presence of “cup-like” morphology of blasts. All cases were additionally analyzed for the FLT3-ITD, and in 122 pts for the FLT3-TKD. Statistical analysis was performed for overall survival (OS), and event-free survival (EFS) according to Kaplan-Meier using the 2-sided log-rank test. Cox regression analysis related OS and EFS with the analyzed parameters. We found a predominance of the FAB M1 (21.3% of all cases), M2 (33.9%), and M4 subtypes (28.3%). Cup-like morphology in ≥5% of all blasts was observed in 39 of 127 evaluable cases (31.3%) confirming previous observations of an association of the NPM1mut and this specific blast appearance. Molecular characterization detected NPM1 mutation subtype A (n=90/122; 73.8%), B (15/122; 12.3%), and D (7/122; 5.7%), which was in accordance to previous studies. In 56 cases (43.8%) there was a coincidence with an FLT3-ITD. Dysplasia of granulopoiesis was detected in 28/126 (22.2%), of erythropoiesis in 28/104 (26.9%), and of megakaryopoiesis in 57/87 (44.5%) cases in which the respective cell lineage could be analyzed. MLD (≥2 dysplastic hematopoietic lineages) was detected in 28 of 105 evaluable cases (21.9%). Clinical follow-up was available in 104 pts. (median follow-up 12,7 months). CR rate was 83.1% in 77 evaluable pts., and median EFS was 42.1 months in 104 evaluable pts (median OS not reached). An additional FLT3-ITD had a significantly inferior OS (p=0.003) and EFS (p=0.007), confirming the present series being representative. However, the presence of MLD was not significantly related to any endpoint such as CR rate, EFS, or OS. There was no association between MLD and the NPM1-subtype. Also, there was no significant correlation of MLD and the presence of a FLT3-ITD. In conclusion, the presence of MLD in AML NPM1mut with normal karyotype had no impact on CR rate and outcome, whereas coincidence of FLT3-ITD significantly worsened prognosis. These results give further evidence that AML with NPM1mut AML is a unique biological entity with clinical course mainly influenced by FLT3-ITD coincidence. These data do not support any additional prognostic influence of MLD in this AML subtype.