ASXL1 mutations are frequent in de novo AML with trisomy 8 and confer an unfavorable prognosis

Acute myeloid leukemia (AML) is a heterogeneous group of genetically diverse hematopoietic malignancies with variable response to treatment. [1] Among the clinical and laboratory characteristics which influence the response to treatment and the survival of patients, cytogenetics at diagnosis represents the most important prognostic variable. Trisomy 8 is one of the most frequent recurring numerical chromosome aberrations in AML, occurring at a frequency of 10%. [2] It presents either as the sole cytogenetic abnormality or in combination with a large variety of different cytogenetic abnormalities. Patients with sole trisomy 8 are mostly classified as having an intermediate prognosis. [3,4] Additional sex combs like-1 (ASXL1) gene, encodes a highly conserved protein that belongs to the enhancer of trithorax and polycombgenes, a gene family with dual functions in both epigenetic activation and repression of gene transcription. [5] Frameshift and stop mutations were found that were predicted to lead to loss of the carboxyterminal plant homeodomain finger on the protein level. [6] ASXL1 mutations (ASXL1-mut) have been detected in about 6–30% of AML. [7–10] Recent reports have demonstrated that ASXL1-mut are more frequent in patients with aberrant karyotype especially in cases with trisomy 8. [11,12] These suggested that ASXL1-mut might play an important role in the patients with trisomy 8. However, the roles of ASXL1-mut in these patients are still unclear. Here, we investigated the occurrence and prognostic impact of ASXL1-mut in AML patients with trisomy 8 aberration. A total of 78 patients with trisomy 8 as the sole aberration or accompanied with other anomalies enrolled from 2007 to 2013 in Jiangsu Institute of Hematology were retrospectively analyzed in this study which was approved by the Ethics Committee of the First Affiliated Hospital of Soochow University following Declaration of Helsinki. The median age was 43 years (12–84 years), and the cohort was all Chinese with the majority of male (51.3%). Historically, analyses have divided patients into favorable, intermediate, and unfavorable cytogenetic groups. [13,14] The same classification scheme was used for this analyses. Here, favorable subgroup consisted of 9 cases with trisomy 8 in combination with t(15;17) or t(8;21), the intermediate group comprised of 41 cases with trisomy 8 as the sole aberration or accompanied with one anomaly which did not include the favorable cytogenetic abnormalities, and the unfavorable category included 28 patients with complex (two or more) aberrations. Only patients of de novo AML with trisomy 8 who received intensive treatment were included into the prognostic analyses. Chromosome analyses were performed according to standard protocols using R-banding. The chromosomes were classified according to the International System for Human Cytogenetic Nomenclature (ISCN, 2005). Genomic DNA was prepared from purified fraction of mononuclear cells after Ficoll density centrifugation. Then PCR amplification of the entire coding region of ASXL1 exon 12 was performed followed by direct bidirectional DNA sequencing. The positive mutation samples were analyzed twice to confirm the results. Only frameshift and nonsense mutations of ASXL1 were analyzed in this study. All statistical analyses were performed using SPSS version 17.0 (SPSS Inc., Chicago, IL). Comparisons of continuous and dichotomous variables were based on the Kruskal–Wallis test and chi-square test respectively. Survival curves were calculated for overall survival (OS) and event-free survival (EFS) according to Kaplan–Meier. Comparisons between groups were based on the twosided log-rank test. Statistically significant tests were identified with p value less than 0.05. The frequency of ASXL1-mut was identified in 19.23% (15/78) of AML patients with trisomy 8 as the sole aberration or accompanied with other anomalies by sequencing