The MLL recombinome of acute leukemias in 2017

Chromosomal rearrangements of the human MLL/KMT2A gene are associated with infant, pediatric, adult and therapy-induced acute leukemias. Here we present the data obtained from 2345 acute leukemia patients. Genomic breakpoints within the MLL gene and the involved translocation partner genes (TPGs) were determined and 11 novel TPGs were identified. Thus, a total of 135 different MLL rearrangements have been identified so far, of which 94 TPGs are now characterized at the molecular level. In all, 35 out of these 94 TPGs occur recurrently, but only 9 specific gene fusions account for more than 90% of all illegitimate recombinations of the MLL gene. We observed an age-dependent breakpoint shift with breakpoints localizing within MLL intron 11 associated with acute lymphoblastic leukemia and younger patients, while breakpoints in MLL intron 9 predominate in AML or older patients. The molecular characterization of MLL breakpoints suggests different etiologies in the different age groups and allows the correlation of functional domains of the MLL gene with clinical outcome. This study provides a comprehensive analysis of the MLL recombinome in acute leukemia and demonstrates that the establishment of patient-specific chromosomal fusion sites allows the design of specific PCR primers for minimal residual disease analyses for all patients.

NPM1, FLT3 and CEBPA mutations in pediatric patients with AML from Argentina: incidence and prognostic value

Mutations in NPM1, FLT3 and CEBPA genes are found in 25-35 % of adult acute myeloblastic leukemia (AML) cases and correlate with prognosis. To date, there have been no reports about these mutations in pediatric AML from Argentina. The aims of the present study were to describe the incidence of NPM1, FLT3 and CEBPA mutations and to analyze their prognostic impact in this population. The incidences of these mutations within a population of 216 pediatric AML cases were: NPM1-mutated 4.2 %, CEBPA-mutated 1.9 %, FLT3-ITD 10.2 % and FLT3-TKD 7.9 %. Among 33 patients with normal karyotype, we found significantly higher frequencies for NPM1-mutated 24.2 % and CEBPA-mutated 12.1 %. Overall survival (pOS) for the 163 eligible non-acute promyelocytic leukemia cases was 46.2 ± 4.3 %, while leukemia-free survival probability was 51.0 ± 4.4 % (n = 135). The NPM1-mutated/FLT3-ITD-negative genotype showed better outcome than any other combined NPM1/FLT3 genotype; this difference was statistically significant within the group of high-risk patients (pOS ± SE 83.3 ± 15.2 % versus 33.1 ± 4.7 %; p = 0.0251). This is the first report of the frequencies of these mutations in Argentina. Despite the limited number of patients, a favorable prognosis of AML with genotype NPM1-mutated/FLT3-ITD-negative was confirmed. This is especially relevant within the high-risk group of patients, as it may contribute to the detection of patients with better prognosis, and thus avoid unnecessary treatment intensification.

New insights to the MLL recombinome of acute leukemias

Chromosomal rearrangements of the human MLL gene are associated with high-risk pediatric, adult and therapy-associated acute leukemias. These patients need to be identified, treated appropriately and minimal residual disease was monitored by quantitative PCR techniques. Genomic DNA was isolated from individual acute leukemia patients to identify and characterize chromosomal rearrangements involving the human MLL gene. A total of 760 MLL-rearranged biopsy samples obtained from 384 pediatric and 376 adult leukemia patients were characterized at the molecular level. The distribution of MLL breakpoints for clinical subtypes (acute lymphoblastic leukemia, acute myeloid leukemia, pediatric and adult) and fused translocation partner genes (TPGs) will be presented, including novel MLL fusion genes. Combined data of our study and recently published data revealed 104 different MLL rearrangements of which 64 TPGs are now characterized on the molecular level. Nine TPGs seem to be predominantly involved in genetic recombinations of MLL: AFF1/AF4, MLLT3/AF9, MLLT1/ENL, MLLT10/AF10, MLLT4/AF6, ELL, EPS15/AF1P, MLLT6/AF17 and SEPT6, respectively. Moreover, we describe for the first time the genetic network of reciprocal MLL gene fusions deriving from complex rearrangements.