PF229 CLUSTER ANALYSIS IDENTIFIES A SPECIFIC IMMUNOPHENOTYPIC PROFILE ASSOCIATED WITH HIGH RISK OF PRIMARY INDUCTION FAILURE AND SHORTER OVERALL AND DISEASE‐FREE SURVIVAL IN NPM1‐MUTATED AML

Abstract

Background:NPM1‐mutated acute myeloid leukemia is a clinically heterogeneous disease entity encompassing different risk categories; despite growing knowledge on the impact of concurrent mutations, part of this biological and clinical heterogeneity is still unexplained. To date, a comprehensive description of the immunophenotypic landscape in NPM1mut AML has never been reported; specifically, the association between specific immunophenotypic patterns and clinical outcome in this AML subset has never been investigated.Aims:We performed a systematic analysis on an NPM1mut AML cohort using a large panel of immunophenotypic parameters in order to identify immunophenotypic clusters sharing common and recurrent features; we then investigated the clinical relevance of the so defined clusters in terms of outcome prediction.Methods:We identified 64 NPM1mut AML cases treated between 2010 and 2018 with intensive chemotherapy. Flow cytometry was performed on diagnostic BM samples in order to fully characterize the immunophenotypic profiles of leukemic populations. We focused our attention on myeloid cells in the CD45dim SSClow blast area. Based on CD34 expression we identified two main cell subsets: CD34+/CD45dim vs CD34‐/CD45dim. The two subgroups were further analyzed by using a comprehensive antigen panel. Parameters were expressed as percentage of positive cells and/or as mean fluorescence intensity; 6 BM samples from healthy donors were used as controls to set normal references.Results:Cluster analysis led to the identification of 3 main immunophenotypic clusters (C1, C2, C3; Fig 2). Distinctive features of C1 were expression of immature antigens (CD117, HLA‐DR) on both CD34+/CD45dim and CD34‐/CD45dim cell compartments as well as recurrent asynchronous CD11b expression and cross‐lineage CD7 and CD25 expression. In C2 a CD34+/CD45dim cell subset was detectable in 46% of patients without significant aberrations. Furthermore, CD34‐/CD45dim population showed an acute promyelocytic leukemia‐like phenotype (CD117‐/+, HLA‐DR‐) albeit with low SSC and CD13dim. In C3 the leading trait was differentiation to monocytic lineage, with low frequency of aberrant antigen expression. Survival analysis by cluster revealed significant differences in terms of DFS and OS (P = 0.006; P = 0.05, respectively; Figure 1A‐B). Most significantly, patients from C1 had a higher relapse risk and a relatively poor outcome when compared to patients classified as C2 and C3. Since the latter categories had a substantially superimposable outcome, we compared patients from C1 to the rest of the population as a unique entity: belonging to C1 cluster correlated with significantly shorter survival (Figure 1C‐D). Along with FLT3‐ITD and age, C1 phenotype emerged as an independent predictor for DFS and OS (Tab 1). While CR rates after first induction cycle were comparable between C1 and Non‐C1 patients, C1 was enriched with patients not achieving CR after 2 or 3 induction cycles (36% vs 11%; P = 0.016; OR 2.024). In multivariate analysis, a C1 profile was the sole predictive factor for not achieving a CR anytime; only 1 patient from C1 could achieve a CR after being refractory to first induction.Summary/Conclusion:Our analysis led to the identification of 3 distinctive immunophenotypic profiles significantly correlated to clinical outcome. Specifically, C1 identified patients at high risk of refractoriness and shorter DFS and OS. These findings shed a new light on the clinical heterogeneity of NPM1mut AML and warrant further investigation from a clinical and biological perspective.image