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Patients with lower-risk myelodysplastic syndromes (LR-MDS) have a generally favorable prognosis; however, a small proportion of cases progress rapidly. This study aimed to define molecular biomarkers predictive of LR-MDS progression and to uncover cellular pathways contributing to malignant transformation. The mutational landscape was analyzed in 214 LR-MDS patients, and at least one mutation was detected in 137 patients (64%). Mutated RUNX1 was identified as the main molecular predictor of rapid progression by statistics and machine learning. To study the effect of mutated RUNX1 on pathway regulation, the expression profiles of CD34 + cells from LR-MDS patients with RUNX1 mutations were compared to those from patients without RUNX1 mutations. The data suggest that RUNX1-unmutated LR-MDS cells are protected by DNA damage response (DDR) mechanisms and cellular senescence as an antitumor cellular barrier, while RUNX1 mutations may be one of the triggers of malignant transformation. Dysregulated DDR and cellular senescence were also observed at the functional level by detecting γH2AX expression and β-galactosidase activity. Notably, the expression profiles of RUNX1-mutated LR-MDS resembled those of higher-risk MDS at diagnosis. This study demonstrates that incorporating molecular data improves LR-MDS risk stratification and that mutated RUNX1 is associated with a suppressed defense against LR-MDS progression.

Azacitidine (AZA) is a hypomethylating drug used to treat disorders associated with myelodysplasia and related neoplasms. Approximately 50 % of patients do not respond to AZA and have very poor outcomes. There is thus great interest in identifying predictive biomarkers for AZA responsiveness. We searched for specific genes whose expression level was associated with response status. Using microarrays, we analyzed gene expression patterns in bone marrow CD34+ cells in serial samples from 32 patients with myelodysplastic syndromes, chronic myelomonocytic leukemia, and acute myeloid leukemia with myelodysplasia-related changes before and during the AZA therapy. At baseline, a comparison of the responders and non-responders showed 52 differentially expressed genes (P