AML Patients with Monosomal Karyotype Are Characterized by Absence of NPM1 and FLT3 Mutations and Worse Clinical Outcome.

The importance of cytogenetics in prognosis of AML is now widely recognized and accepted in clinical practice. A recent study found that autosomal chromosomal monosomy predicted for an adverse outcome. The goal of this study is to characterize patients with monosomal karyotype by mutation status and clinical features.

One-hundred forty consecutive AML patients diagnosed at Stanford University Hospital between 2005 and 2008 with adequate material for mutation analysis were studied. Cases were classified using the 2008 WHO criteria. Diagnostic cytogenetic findings were reviewed and patients were stratified into risk groups using Southwest Oncology Group criteria. An abnormality was considered clonal when at least two metaphases had the same aberration, except for clonal monosomy, which required at least three metaphases. The karyotype analysis was based on 20 or more metaphases. All samples were tested for NPM, FLT3 (ITD and D835) and CEBPA mutations. Clinical parameters including hemogram data at time of diagnosis were reviewed. Clinical follow-up including overall survival (OS), progression free survival (PFS) and complete remission (CR) rates were retrospectively determined. Kaplan-Meier methods and univariate Cox proportional hazards regression analysis were used to compare the clinical data.

The cases included 77 males and 63 females with a median age of 58 (range 17-83). Cytogenetic risk-group stratification resulted in 14 patients with favorable, 88 with intermediate and 28 with unfavorable risk status. Loss of one or more autosomal chromosomes was present in 18 /130 patients (13.8%) with available cytogenetic studies. A single autosomal monosomy was found in 5 patients while 13 patients had two or more autosomal monosomies. The most common chromosomes lost in these 18 patients included 7 (55% of 18 cases), 5 (50%), 17 (33%), 21 (22%), 20 (22%), 22 (17%) and 18 (11%). Using the 2008 WHO criteria, there were 66 AML with myelodysplasia-related changes (AML-MRC), 55 AML not otherwise specified (AML-NOS), 14 AML with either t(8;21), inv(16) or t(15;17) and 5 therapy related AMLs. Overall, 35 patients (25% of all patients) had a NPM1 mutation (19 of which were FLT3 mutated), 33 had FLT3-ITD mutation (24%), 11 had FLT3-D835 (8%) and 11 had a CEBPA mutation (8%) (4 of which were FLT3 mutated). Patients with monosomal karyotype were significantly older (83 vs. 59 years, p=0.0125) and presented with lower WBC (34 vs. 66 K/uL, p=0.0006), lower platelets (41 vs. 64 K/uL, p=0.0111), and lower blasts (38% vs. 65%, p=0.0030) as compared to the rest of AML patients. In addition, patients with monosomal karyotype were more frequently diagnosed with AML-MRC (16/18 vs. 48/107, p=0.0034) and exhibited a decreased frequency of NPM1 mutation (0/18 vs. 28/107, p=0.0138) and FLT3-ITD mutation (0/18 vs. 29/107, p=0.0117). Clinical outcome data showed that patients with monosomal karyotype had a significantly worse OS, PFS and CR compared to the rest of AML patients (OS p=0.001, PFS p=0.002 and CR p=0.0262). Dividing patients by number of monosomies showed that patients with 2 or more monosomies had a significantly worse OS (p=0.0001) and PFS (p=0.0045) than patients without any monosomies. However, no difference in OS or PFS was seen when comparing patients with 1 monosomy to those with 2 or more monosomies. Within the AML-MRC group, monosomal karyotype correlated with lower WBC (17 vs. 37 K/uL, p=0.0005), lower platelets (21 vs. 35 K/uL, p=0.0095), lower blasts (19% vs. 36%, p=0.0015) and shorter OS (p=0.0322) and PFS (p=0.0084).

AML patients with monosomal karyotype exhibit a significantly worse OS, PFS and lower CR as compared to other AML patients. Most of patients fall within the newly defined AML-MRC group and are characterized by significant absence of NPM1 and FLT3-ITD mutations.

No relevant conflicts of interest to declare.