Frequency and Clinical Impact of Cytogenetic Clonal Evolution in Myelodysplastic Syndromes (MDS) with Isolated Del(5q)

Introduction: Inmyelodysplastic syndromes (MDS) the karyotype is one of the most important predictor of disease advancement, response to the treatment and patients' outcome. Clonal cytogenetic abnormalities are detected in the bone marrow cells in approximately 50% MDS patients. The interstitial deletion of the long arm of chromosome 5-del(5q)-is the most common finding, accounting for roughly 30% of abnormal karyotypes. According to IPSS-R, MDS with isolated del(5q) are associated with a favorable clinical course and are recognized as a specific subtype of MDS. However in some cases, acquisition of additional genetic aberrations may occur during the course of the disease and it has been proved it negatively influences outcome of MDS patients. The aim of the study was: (1) to evaluate the frequency of cytogenetic clonal evolution during the course of the disease in MDS patients with isolated del(5q), (2) to analyze the pattern of acquired cytogenetic abnormalities, and (3) to assess the impact of clonal evolution on transformation to acute myeloid leukemia (AML) and/or overall survival (OS).

Patients and Methods: A detailed retrospective and/or prospective genome-wide analysis of fixed bone-marrow cells of 184 adults with del(5q), identified with conventional G-banding at the diagnosis of MDS, was performed during the course of their disease. The chromosomal aberrations were studied through FISH with Vysis DNA probes (Abbott, Des Plaines, IL) and mFISH/mBAND methods using the 24XCyte and the XCyte color kits (MetaSystems, Altlussheim, Germany). Genomic imbalances were identified with CytoChip Cancer SNP 180K (BlueGnome, Cambridge, UK) or with Illumina Human CytoSNP-12 arrays (Illumina, San Diego, CA). Amplicon deep sequencing of TP53 mutations (exons 4-11) was performed on a Roche 454 GS Junior system (Roche, Indianapolis, IN) using oligonucleotide primer plate assays validated according to the IRON-II (Interlaboratory Robustness Of Next generation sequencing).

Results: Cytogenetic clonal evolution was observed in 21/184 MDS patients with isolated del(5q) (11.4%). Abnormalities most frequently acquired during the course of the disease were non-balanced rearrangements involving chromosomes 5, 7, 3, 17, 12 and 11. Deleted chromosome 5 was highly unstable and was often involved in different types of cryptic unbalanced rearrangements (translocations, insertions). Fragmentation of 5q was present as well.Clonal evolution was frequently associated with TP53 mutations and/or unbalanced aberrations of 17p.The median time between the first and the last evaluation was 23 months (range 2-83 months). Clonal evolution was detected between 2 and 83 months (median 14 months) after first cytogenetic evaluation. Median OS was 35 months (range 6-89 months), median survival from the first emergence of cytogenetic clonal evolution was 7.5 months (range 1-31 months). Progression to RAEB 1 or RAEB 2 was detected in 10 patients, 11 patients transformed into AML.

Conclusions: Clonal evolution was detected in 11.4% of patients with MDS and isolated del(5q). The pattern of acquired abnormalities was similar to the changes previously described in high risk MDS at primary evaluation. The emergence of specific clones with additional genetic aberrations frequently correlated with altered clinical parameters. Cytogenetic clonal evolution was strongly associated with higher frequency of loss of heterozygosity (LOH) of 17p and/or TP53 mutations, shorter OS, rapid disease progression and transformation to AML. This data substantiate a need for regular molecular cytogenetic monitoring to guide clinical treatment decision in MDS with isolated del(5q).

This study was supported by research projects RVO-VFN64165, GACR P302/12/G157, PRVOUK-P27/LF1/1, and MHCR 00023736.