An Accumulation of Cytogenetic and Molecular Genetic Events Characterizes the Progression From MDS to Secondary AML: An Analysis of Paired Samples in 38 Patients Analyzed by Cytogenetics, Mutation Analysis and SNP Microarrays.

Abstract

Abstract 1748Poster Board I-774A hallmark of myelodysplastic syndromes (MDS) is their progression to acute myeloid leukemia (AML). Even though the pathogenetic mechanisms underlying both MDS and de novo AML have broadly been studied on a genetic level, the molecular factors that determine the progression from MDS to secondary AML (s-AML) are largely unknown. In order to gain further insights into the underlying genetic events leading to progression from MDS to AML, we analyzed a total of 38 patients at both their MDS and s-AML disease state focusing on cytogenetics and mutations in NPM1, MLL, NRAS, RUNX1 and FLT3. Additionally, we performed genome-wide SNP microarray analyses (Affymetrix SNP Array 6.0) at both timepoints of investigation in a subset of 34/38 patients. The cohort comprised 38 MDS patients (male/female: 25/13; median age at diagnosis 69.5/range 29.2-82.9) representing WHO categories RARS (n=2), RCMD (n=3), RAEB-1 (n=11), RAEB-2 (n=8), MDS unclassifiable (n=9), CMML (n=3) and MDS/MPN overlap (n=2). Most patients presented in MDS phase with a normal karyotype (n=27; 71%) or showed a single cytogenetic abnormality (n=8). One patient had two alterations and two patients showed a complex karyotype. Molecular genetic analysis revealed the presence of MLL-PTD (n=2), NRAS (n=2) and RUNX1 (n=10, 26.3%) mutations, with mutations in RUNX1 being by far the most common molecular mutation detected in our MDS cohort. NPM1 and FLT3-ITD mutations were not seen at that stage. The median time between analysis of MDS and the diagnosis of s-AML was 269 days (range 40 to 1044). Progression to s-AML was defined by blasts in the bone marrow or peripheral blood >20% and was accompanied by accumulations of either cytogenetic or molecular genetic events. 10/38 patients showed increased cytogenetic complexity with gains of one to 10 aberrations in the course of disease evolution (median number of gained anomalies: 1). Three patients acquired trisomy 8 during disease progression. Moreover, individually different chromosomal losses (n=1), insertions (n=1), translocations (n=3) and further chromosomal gains (n=8) were detected. 16 additional molecular alterations were observed in 15/38 patients involving genes NPM1 (5/16), MLL (3/16), NRAS (3/16), RUNX1 (3/16) and FLT3-ITD (2/16). Of note, these patients exclusively showed either cytogenetic or molecular genetic progression. Only one patient acquired both cytogenetic abnormalities (del(5q) and del(7q)) and a new mutation in RUNX1. 12/38 patients did neither show cytogenetic progression nor did they gain mutations in the genes analyzed. The latter patients, however, showed a trend towards a better overall survival from time of diagnosis of s-AML when compared to the patients with progression markers (median overall survival: not reached vs 7.9 months, % surviving at 1 year: 87.5 vs. 49.7%, p=0.09). SNP microarray analyses revealed the presence of UPD (uniparental disomy) in 11/34 paired samples including chromosomal regions 2p, 4q (n=2), 7q, 11q, 12p, 13q, 17q, 19p, 19q and 21q. While 9/11 patients showed the same UPD at both their MDS and s-AML stages, UPD21q (upd(21)(q11.2-qter)) in one and UPD17q (upd(17)(q21.2-qter)) as well as UPD19q (upd(19q13.42-qter)) in another patient were acquired during disease progression. Interestingly, UPD21q acquired during disease progression coincided with a shift from heterozygous to a homozygous RUNX1 mutation suggesting a role for acquired UPD as a mechanism leading to copy-neutral loss of heterozygosity of RUNX1. UPD(4q) came along with a mutation in TET2, which is located on 4q. This mutation was already present at the MDS stage. In conclusion, our data provide evidence for a multistep pathogenetic mechanism in the progression from MDS to s-AML. Patients can be grouped in two categories; they either acquire cytogenetic aberrations or present a higher number of molecular genetic mutations. While RUNX1 mutations already occurred at a high frequency at the MDS stage, mutations in NPM1 and FLT3 were seen only after progression to s-AML. DisclosuresFlach:MLL Munich Leukemia Laboratory: Employment. Schindela:MLL Munich Leukemia Laboratory: Employment. Dicker:MLL Munich Leukemia Laboratory: Employment. Schnittger:MLL Munich Leukemia Laboratory: Equity Ownership. Kazak:MLL Munich Leukemia Laboratory: Employment. Kohlmann:MLL Munich Leukemia Laboratory: Employment. Kern:MLL Munich Leukemia Laboratory: Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Equity Ownership. Haferlach:MLL Munich Leukemia Laboratory: Equity Ownership.