Flow-Cytometric Minimal Residual Disease Determination Is a Surrogate Prognosticator in Adult AML Patients Lacking Specific Molecular Signatures.
Authors: Buccisano Francesco , Maurillo Luca , Del Poeta Giovanni , Del Principe Maria Ilaria , Fraboni Daniela , Ammatuna Emanuele , Consalvo Maria Irno , Panetta Paola , Ottaviani Licia , Faccia Sabrina , Rizzo Manuela , Postorino Massimiliano , Cantonetti Maria , Lo Coco Francesco , Amadori Sergio , Venditti Adriano 
Published: October 2019

Abstract
In a remarkable proportion of adult AML patients (40–50%), no clonal abnormalities are found on standard cytogenetic analysis. In this group of patients, several gene mutations have been described, allowing to discriminate subgroups with distinct clinical outcome. Among these molecular signatures, FLT3, a receptor tyrosine kinase with important roles in hematopoietic stem/progenitor cell survival and proliferation, has been demonstrated to be mutated in about 1/3 of AML cases, identifying a subgroup of patients characterized by disappointing overall cure rates. Therefore, roughly 60% of patients with normal karyotype are not classifiable by this specific mutation. The purpose of the present study was to investigate, in this group of patients with no specific molecular signature the prognostic role of MRD as determined by multiparametric flow-cytometry (MPFC). We analyzed a group of 127 AML cases entered into the EORTC/GIMEMA protocols AML10/AML12 (age <61yrs) or AML13/AML15/AML17 (age >61 yrs). By applying the maximally selected log-rank statistics, the threshold discriminating MRD negative from positive cases was set at 3.5 x10−4 residual leukemic cells, a level that selected, at the post-consolidation time-point, two groups of patients with distinct prognosis. Seventy-two out of 127 (56%) had a normal karyotype. Among these 72, 53 were studied for FLT3 mutational status; in 13 (25%) a mutated variant of FLT3 was detected. Among the remaining 40 patients with normal karyotype and unmutated FLT3, 39 were evaluable for the MRD status at the post-consolidation time-point: 9 patients were MRD− and 30 MRD+. These two subsets showed a distinct outcome in terms of 5-years RFS (83 vs. 23%, p=0.031). Interestingly, the FLT3−MRD+ patients shared with those FLT3 positive a similar poor prognosis (Figure 1). In recent reports, the evaluation of outcome depending on FLT3 status has been integrated with the analysis of the mutated status of other genes: FLT3-mutated cases associated frequently with Nucleophosmin (NPM1) exon-12 gene mutations but rarely with other mutations. The favorable impact of NPM1 mutations on OS and EFS clearly emerged in the group of normal-karyotype AML without FLT3 mutations. In a subset of 44 patients of our series either the mutations were investigated; this combined analysis identified 8 out of 44 (18%) patients FLT3 unmutated/NPM1 mutated with a better outcome (5-years OS 50% and RFS 50%, respectively) as compared to FLT3 unmutated/NPM1 unmutated and FLT3 mutated patients, which was however poorer than that of FLT3 unmutated/MRD− cases (Figure 1). In conclusion, MRD determination at the post-consolidation phase may help at improving the prognostic assessment of AML patients lacking specific chromosomal and/or molecular lesions, allowing risk-adapted post remissional therapies to be designed with more accurate modalities.
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