ALBERT

Beschreibung: Introduction: Myelodysplastic syndrome with del5q (MDSdel5q) is the only cytogenetically defined MDS category recognized by WHO in 2001, 2008 and 2016 and is defined as a MDS with deletion on the long arm of chromosome 5 and less than 5% of blast cells in bone marrow. It is known that for patients with MDSdel5q and transfusion dependence (TD), Len (LEN) is the first choice of treatment. However, data regarding factors that may impact on the development of TD or disease evolution in patients diagnosed without TD are scanty. In our study a retrospective multicenter analysis on patients with low-int 1 MDSdel5q without TD at diagnosis has been performed in order to answer these questions. Patients and methods: We performed a multicenter collaborative research from the Spanish (RESMD) and German MDS registries. Data from 153 low risk MDSdel5q without TD at diagnosis were retrospectively analyzed. Statistical analysis: Data were summarized using median, range, and percentage. The event of TD was defined as the development of TD according to the IWG criteria (2006) and/or the beginning of a treatment which could modify disease course (LEN or ESA). Transfusion or treatment free survival (TFS), overall survival (OS) and leukemia free survival (LFS) were measured from diagnosis to TD or treatment, the first occurred (or to last follow up if none), last follow up or death from any cause and evolution to AML, respectively. TFS, OS and LFS were analyzed using the Kaplan Ð Meier method. The Log-rank test was used to compare variables and their impact on survival for univariate analysis.Multivariate analysis was performed using Cox's proportional hazards regression model. For comparison of Kaplan Meier curves the long rank test was used, with statistical significance with p350 109/L) (p=0.007), and neutropenia (

Beschreibung: Background and aim: Inflammasome and pyroptosis overactivation have recently been associated as fundamental mechanisms in the ineffective hematopoiesis of myelodysplastic syndromes (MDS). Chronic myelomonocytic leukemia (CMML) shares histological and clinical characteristics with MDS but, within clinical differences, It stands out a high association with inflammatory/autoimmune diseases in which a disproportionate activation of inflamasome has been implicated. Our hypothesis is that CMML cases show a higher inflammasome activation with respect to the MDS subset, a relevant difference both in terms of potential therapeutic targets and pathogenic clues. The main objective is to confirm, describe and quantify these differences using high-performance and multi-gene/protein methods. Methods: We performed enhanced RNA-seq in bone marrow mononucleated cells of 27 CMML at diagnosis, 10 MDS and 9 controls (103 million average readings). We selected 116 genes related to the inflammasome and reviewed the differential expression between cases and controls. We evaluated by multiplex immunoassay the profile of 28 cytokines in peripheral blood in 35 CMML patients, 37 MDS and 8 controls. Subsequently, we studied whether these differentially expressed genes / cytokines showed differences in CMML depending on the mutational state of TET2, SRSF2 and ASXL1. Finally, we compared in vitro the degree of activation of inflamasome in the monocytoid component of 8 CMML patients versus 7 controls. Results: In the transcriptomic analysis of the inflamasome genes in patients with CMML, we found 30 of 116 differentially expressed genes compared with healthy controls. Of those 30 genes, 26 showed a pro-inflammatory function and, of them, 18 were up-regulated. Of the 4 differentially expressed genes with an anti-inflammatory function, 3 were significantly under-expressed in CMML patients. We highlight, due to the quantitative difference, the overexpression of two genes coding for monocyte chemotactic proteins, CCL7 and CCL2 (FC = 269.21, p = 0.032; FC = 11.79, p = 0.03) That pro-inflammatory transcriptional profile was not so evident in the cases of MDS: of the 29 differentially expressed genes with pro-inflammatory function, 18 were down-regulated. Subsequently, we designed a customized panel for proteomic analysis including 9 of the 30 differentially expressed genes in CMML. We found that, in a relevant percentage of cases, also proinflammatory cytokines derived from these differentially expressed genes were elevated (62.5%) in peripheral blood of patients, compared to healthy donors; pointing towards the key role of gene transcription in the definition of the pro-inflammatory sense of the proteomic dimension of inflammasome in CMML. Next, we found that those patients with CMML and somatic mutations of TET2 had a higher expression of CCL7 and CCL2 compared to patients with CMML wild type, with a tendency to significance in the first case and significant in the second (FC 11.9, p = 0.15; FC 7.8, p = 0.03). Finally, we conducted in vitro stimulation studies at diagnosis in patients with CMML confirming that the canonical activation of the NLRP3 inflammasome (increased production of IL-1β) is significantly enhanced with respect to control individuals. Conclusion: We describe for the first time, a hyperactivation in CMML, compared with MDS, of the components of the inflammasome. Hyperactivation associated in CMML to a gene transcriptional mechanism and related, in the case of the two most over-expressed genes, CCL2 and CCL7, to the presence of mutations in TET2. Our findings point to new therapeutic targets whose modulation could restore inefficient hemopoiesis and potential diagnostic and prognostic biomarkers in CMML. Disclosures Díez-Campelo: Celgene Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding. Jerez:Novartis: Honoraria; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees.

Beschreibung: Background: Lenalidomide (LEN) is a reference treatment in IPSS low and in1 (lower) risk MDS patients with isolated de(5q) (MDS-del(5q)) and RBC - TD. Most low risk MDS-del(5q) patients with anemia and independent of transfusions develop TD or need of treatment for symptomatic anemia very early after diagnosis (median time to transfusion/treatment of 20 months, López Cadenas et al abstract 3180 ASH, 2016). LEN directly targets the del(5q) clone improving anemia, quality of life and survival in this subset of patients. Limited data also suggest a role of LEN in non-TD patients with del(5q) (Oliva et al Cancer Med 2015). However no prospective randomized study of LEN has been performed in this group of patients. Material: The Sintra-Rev clinical trial is a phase III European multicenter study, in low-risk MDS-del(5q) patients, with anemia (Hb

Beschreibung: Myelodysplastic syndromes (MDS) are clonal hematopoietic stem cell (HSC) malignancies characterized by ineffective hematopoiesis. Genetic alterations do not fully explain the molecular pathogenesis of the disease, indicating that other types of lesions, such as transcriptional aberrations, may play a role in its development. Moreover, MDS prevalence is almost exclusive to older patients, suggesting that elderly-related alterations may predispose to the development of this clinical entity. Thus, study of the transcriptional lesions occurring in the aging-MDS axis could shed some light of the molecular bases of the disease. To characterize the transcriptional profile of HSCs in aging and MDS, we isolated CD34+, CD38-, CD90+, CD45RA- cells from 11 untreated MDS patients with unilineage and multilineage dysplasia (median of 75 y/o), as well as from 16 young and 8 elderly healthy donors (median of 21 and 70 y/o, respectively), and their expression profile was analyzed using MARS-seq. Unsupervised principal component analysis demonstrated that the three groups of HSCs clustered separately, indicating that different expression profiles characterize healthy young and elderly, and MDS-associated HSCs. To better understand the gene expression deregulation of HSCs, we analyzed the transcriptional dynamisms along the aging-MDS axis, detecting groups of genes following different patterns of expression. Some gene clusters showed exclusive alteration either in aging or in the progression from elderly HSCs to MDS-HSCs, other groups of genes presented a continuous alteration along the axis, and some displayed opposite regulation in aging and in the transition to MDS (Figure 1). Genes showing specific downregulation in aging were involved in DNA damage sensing and repair, and in cell cycle regulation, whereas genes overexpressed in this process were enriched in apoptosis regulators and in cancer-associated genes, including AML-related factors. These findings indicate that transcriptional changes in aging may predispose for MDS and AML, and potentially other malignancies. Interestingly, we detected a group of genes in which the age-mediated upregulation of gene expression was reversed to that of young HSCs in MDS, indicating a "rejuvenation" profile of malignant HSCs. These genes were involved in response to inflammation, to different types of stress conditions such as hypoxia or radiation, and to cytokines. Elderly HSCs may upregulate such genes in response to the known inflammatory microenvironment of elderly bone marrow. Intriguingly, the decrease in expression detected in MDS suggests that malignant HSCs lose the ability of reacting to such stimuli, possibly favoring their survival in a hostile microenvironment. Finally, the analyses performed allowed for the identification of genes showing MDS-specific deregulation. Genes specifically overexpressed in MDS compared to normal (both young and elderly) HSCs, we enriched in transcriptional and epigenetic regulators, and among them, we detected the presence of DDIT3/CHOP, a member of the CCAAT/enhancer-binding protein (C/EBP) family of transcription factors. To determine its potential effects on hematopoietic deregulation, DDIT3 was exogenously overexpressed in healthy HSCs. Notably, its upregulation produced an erythroid bias in an ex-vivo differentiation system, with an increase in the percentage of erythroblasts and a decrease in granulocytes and monocytes compared to HSCs transduced with the empty vector. Transcriptomic analysis of transduced HSCs not subjected to differentiation demonstrated how DDIT3 overexpression produced an erythroid-prone state of HSCs, suggesting it may act as a pioneer factor in MDS-HSCs. Furthermore, gene set enrichment analysis showed that DDIT3 overexpression produced an MDS-like transcriptional profile, suggesting this factor may be key in the acquisition of the disease. Altogether, our results demonstrate that HSCs undergo transcriptional changes in the aging-MDS axis that may alter their intrinsic functions as well as their response to the microenvironment, ultimately contributing to the acquisition of the disease. In particular, our data show that DDIT3 may be a potential driver of MDS transformation. Disclosures Paiva: Amgen, Bristol-Myers Squibb, Celgene, Janssen, Merck, Novartis, Roche, and Sanofi; unrestricted grants from Celgene, EngMab, Sanofi, and Takeda; and consultancy for Celgene, Janssen, and Sanofi: Consultancy, Honoraria, Research Funding, Speakers Bureau. Díez-Campelo:Celgene Corporation: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Research Funding.

Beschreibung: Background: The 2016 reviewed classification of the World Health Organisation (WHO) defines a group of myelodysplastic/myeloproliferative neoplasms (MDS/MPN) including the chronic myelomonocytic leukemia (CMML), the myelodyplastic syndrome with ring sideroblasts and thrombocytosis (MDS-RS-T) and the MDS/MPN unclassifiable (MDS/MPN-U). The presence of typical clinical characteristics of MDS and MPN hinders the diagnosis and the prognosis of MDS/MPN-U. Aim: The objective of this study was to compare the clinical characteristics and the prognosis of a series of patients with MDS/MPN such as CMML, MDS-RS-T and MDS/NPM-U from the Spanish registry of MDS. Method: We analized 107 patients diagnosed with MDS/MPN (MDS-RS-T, MDS/NPM-U and CMML) according to the 2016 WHO classification. A comparison of the clinical characteristics, overall survival (OS) and cumulative incidence of progression (CIP) was performed. Results: Median (range) age was 74 (23-93) years and 68/107 (64%) were males. The number of patients in each group was: MDS-RS-T (n=45), MDS/MPN-U (n=29) and CMML (n=33). The main clinical characteristics of the three groups are described in Table 1. There were significant statistical differences in hemoglobin and lactate dehydrogenase levels and leukocyte, monocyte and platelet counts between the three groups. With a median (range) of follow-up of 3.1 (0.3-19.3), 3.7(0.7-10.4) and 4 (1.8-8.5) years for MDS-RS-T, MDS/MPN-U, and CMML, respectively, the OS (95%CI) at 5 years was significantly better in patients with MDS-RS-T (61% [42%; 80%]) compared to MDS/MPN-U and CMML patients (21% [1%; 41%] and 19% [3%; 35%], p=0.002) (Figure 1). The CIP (95%CI) at 5 years between the three groups was significantly different: MDS/MPN-U and CMML (40% [18%; 61%] and 32% (14%-52%, respectively) vs. MDS/RS-T 8% [0.4%; 30%]) (p=0.005) (Figure 2). Conclusions: 1) In this series of patients with MDS/MPN (MDS-RS-T, MDS/MPN-U and CMML) according to the 2016 WHO classification clinical characteristics were similar except for hemoglobin and lactate dehydrogenase levels and leukocyte, monocyte and platelet counts. 2) Patients with MDS-RS-T had longer OS and less CIP than those with MDS/MPN-U and CMML; 3) The prognosis of MDS/MPN-U and CMML were similar. Supported by grants from: AGAUR 9015-470120/2015, 2017-SGR288 (GRC), CERCA Program from Generalitat de Catalunya, and "La Caixa" Foundation. Disclosures No relevant conflicts of interest to declare.

Beschreibung: Introduction:Cardiovascular disease (CVD) is an important cause of morbimortality in patients with low risk myelodysplastic syndrome (LR-MDS). Up to 70% of patients suffer cardiovascular events and heart disease is the second cause of death in this context. Cardiac damage etiology is complex and multifactorial in this group of patients. Iron overload cardiomyopathy (IOC) due to transfusion dependency is the most well identified factor in this setting, however other circumstances such as vascular aging, cardiac reserve reduction and high cardiac output related to chronic anemia, among others, play an important role in this population. Thus, despite its importance in MDS patients, prognostic cardiovascular predictive factors are not adequately identified, and cardiac monitoring in these patients is not sufficiently stablished. Therefore, our objectives were to determinate the prevalence and characterization of CVD in LR-MDS patients, to analyze their mortality and cardiovascular prognosis and to identify predictors of cardiovascular events or death (combined event, CE) in this setting. Material and methods: A prospective single center study with 36 LR-MDS patients (31 of them in transfusion requirements) was conducted. All patients underwent a complete hematological and cardiological assessment including ECG, cardiac biomarkers (N-terminal pro b-type natriuretic peptide (NT-proBNP) and high-sensitive cardiac T troponine (hs-cTn)) and cardiac magnetic resonance (CMR) with parametric sequences (T1, T2 and T2* mapping) and myocardial deformation by feature tracking (FT). Univariate and multivariate analysis including clinical, analytical and imaging factors for predicting the combined cardiovascular event (heart failure (HF), arrhythmia or ischemic heart disease) and/or all-cause of mortality (CE) was performed by Cox regression. Results:Thirty-six patients with LR-MDS were recruited from 2016 to 2017, with a mean age of 76 ± 10 years, 53% males. Thirty-one patients (84%) were in transfusion dependency (TD). Regarding baseline characteristics for cardiovascular disease most of them (90.9%) had CV risk factors (CVRFs) and 36% suffered of previous heart disease (Baseline characteristics, hematological and cardiac situation at inclusion in table 1). Cardiac assessment revealed high prevalence of structural heart disease, in most of cases previously unknown and significant incidence of CV events during the follow-up. Thus, Cardiac MR detected high prevalence structural heart disease (table 2). As a result of this first cardiac assessment, 15 patients (42%) required modifications in their cardiovascular treatment and most of cases needed to start cardiovascular treatment. After a median follow up of 2.2 years, 35.5% of TD patients suffered the CE, 16% died and 32% presented cardiovascular events: HF 13.9%, pacemaker implantation due to atrioventricular block 2.8%, ischemic heart disease 5.6%, and atrial fibrillation 5.6%. In the univariate analysis for the CE (table 3), higher hs-cTn (p=0,007), higher NT-proBNP (p = 0.001), T2*

Beschreibung: INTRODUCTION: In the rituximab era, the prognostic influence of bone marrow (BM) infiltration in patients with diffuse large B-cell lymphoma (DLBCL) has been hardly studied. In this retrospective observational study, we aim to investigate the prognostic influence of concordant and discordant BM infiltration in patients with histological diagnosis of DLBCL. In addition, we analyzed the possible clonal relationship between BM and lymph node tumor cells in the cases with discordant histology. PATIENTS AND METHODS: All patients diagnosed of DLBCL in our center from January 1, 1999 were included in the study. Histological BM infiltration pattern was classified as concordant (DLBCL infiltration) or discordant (small or low-grade B-cell lymphoma) based on the diagnostic reports from the Pathology department. All cases were reviewed for this purpose by an expert pathologist. To further characterize the discordant cases, flow cytometry (FCM) reports of BM infiltration were reviewed. In the discordant cases, the clonal IGH rearrangement was studied in both BM and lymphadenopathy, by amplification of the VDJ genes as recommended in the BIOMED-2 protocol. For survival analysis, only patients treated with R-CHOP or similar were included. RESULTS: 236 patients diagnosed of DLBCL were included in the study; of them, 31 (13%) had concordant histological BM infiltration and 18 (7.6%) discordant. Phenotypic characterization by FCM of the discordant cases was heterogeneous: chronic lymphocytic leukemia (N = 2), follicular lymphoma (N = 5), marginal zone lymphoma (N = 2), non-specific phenotype (N = 5) or non-infiltration (N = 2). Clonality studies were performed in the discordant cases. Good quality DNA was obtained in 17 out of 18 patients. We confirmed the same clone in both BM and lymphadenopathy in 12 patients (70%); different clones were observed in two, and a polyclonal pattern was obtained in the remaining three patients. Survival analyzes were conducted only in the 186 patients treated with R-CHOP or similar. With a median follow up of 58 (1-135) months, PFS was significantly worse in patients with concordant (35% at 5 years, p = 0.001) or discordant (35% at 5 years, p = 0.04) histology, compared to patients without infiltration (64% at 5 years) (Figure 1). OS was significantly lower in patients with concordant histology (53% at 5 years, p = 0.05), whereas there was no significant difference between patients with discordant infiltration (62% at 5 years, p = 0.8) and non-affected BM (75% at 5 years). In the multivariate analysis, concordant BM infiltration (HR = 2.25, 95% CI 1.2 to 4.3, p = 0.01) had a negative influence on PFS (but not on OS), independently of the age, ECOG and LDH, while discordant histology was close to statistical significance (RR = 2; 95% CI 0.95 to 3, p = 0.1) CONCLUSIONS: Our results indicate that BM infiltration, both concordant and discordant, is associated with a lower PFS in DLBCL patients treated with R-CHOP or similar. Cases with discordant BM infiltration have a very heterogeneous phenotype, but we found a clonal relationship between the two different histologies in a high proportion of cases, indicating a probable histologic transformation from a low-grade lymphoma. Further studies are needed to determine the sequence of biological events that might be involved in this transformation. Figure 1. Progression free survival (PFS) according to the concordant or discordant histology of the BM Figure 1. Progression free survival (PFS) according to the concordant or discordant histology of the BM Disclosures No relevant conflicts of interest to declare.

Beschreibung: Background and Aim:It is increasingly recognized that patients with a de novomyelodysplastic syndrome (MDS) onset as young adults, lacking any other feature of a congenital disorder, may share a pathogenic overlap due to the presence of both germline and somatic variants. Identifying an inherited pathogenic variant has important therapeutic implications beyond family counselling: adapting the selection of sibling donor, the use of highly cytotoxic therapy and the monitoring for other cancer development. However, most studies have focused on patients with suspected inherited disorders based on the presence of physical abnormalities and/or family history. In addition, a mixture of pediatric and adult cases is usually reported. The aim of this study is to characterize the germline and tumor variants in a group of adult MDS patients without accompanying congenital physical anomalies and or family antecedent of bone marrow failure. Methods: We included 72 patients from 15 Spanish centers with a diagnosis of MDS between 18 and 60 years old (y.o). Patients with a previously diagnosed or suspected (one physical anomaly or family history) congenital syndrome were excluded. Diagnoses were made in accordance with the WHO 2016 classification. Whole-exome sequencing (WES) libraries were prepared using SureSelectXT Target Enrichment and sequenced on a HiSeq4000 platform (IlluminaInc.). Mean number of reads per sample was 138,726,017 with a Phred Quality Score 〉30 in 95.05% of bases. Read mapping sequence alignment and variant calling were performed using Biomedical Workbench (Qiagen). WES was performed on 72 tumor and 32 paired germinal DNA (buccal swab). To identify potential germline-causal mutations, a selection tool was implemented incorporating 239 genes associated with cause or predisposition to bone marrow failure or cancer. Variants with an ExAC, TOPMed and/or European 1000 Genomes minor allele frequency ≥0.01 were discarded. Results: The median age at diagnosis was 49 y.o. The cohort was categorised into two groups, less or equal 50 y.o. (62.5%) and between 50 and 60 y.o. (37.5%). In the first group, the frequency according to the WHO classification were 12% MDS with single lineage dyplasia (MDS-SLD), 8% MDS with ring sideroblasts (MDS-RS), 11% MDS with multilineage dyplasia (MDS-MLD), 24% MDS with excess blasts(MD-EB), 4% MDS with isolated del(5q)(MDS-del5q), 4% MDS unclassifiable and 4% chronic myelomonocytic leukemia (CMML). Meanwhile, in the group with age more than 50 y.o., the subtypes were 3.7% MDS-SLD, 7.4% MDS-RS, 29.6% MDS-MLD, 40.7% MD-EB, 3.7% MDS-del5q, and 14.8% CMML.Patients less or equal 50 y.o. were stratified based on IPSS-R as very low (4%), low (64%), intermediate (20%), high (12%) and very high (0%); and the group of more than 50 y.o. as very low (14.8%), low (33.3%), intermediate (29.6%), high (11.1%) and very high (11.1%).The mean number of somatic mutations was 0.68 in patients with less or equal 50 y.o. and 1.37 in those between 50 and 60 y.o., p=0.033 (U Mann-Whitney); and regarding germline variants, the first group mean number was 2.44 (p25-75, 1-3) and the second group showed a mean of 1.85 (QI 25-75, 1-3), p= 0,331.In the whole cohort, germline variants were found in 62 out of 72 patients, with the following frequencies: ATR(N=5, 6.9%), followed by BARD1(N=5, 6.9%), ERCC6L2(N=4, 5.6%), MSH6(N=4, 5.6%), TCIRG1(N=4, 5.6%), NBEAL2(N=4, 5.6%), ASXL1(N=3, 4.2%), ATM(N=3, 4.2%), MPL(N=3, 4.2%), NF1(N=3, 4.2%), RECQL4(N=3, 4.2%), SAMD9L(N=3, 4.2%), WRN(N=3, 4.2%).Among germline variants, those reported previously as pathogenic or likely pathogenic, or involving genes associated with familial MDS/AML included: ERCC6L2(N=4, 5.6%), SAMD9L(N=3, 4.2%), and one case mutated for DDX41, FANCC, JAK2, MSH6, SETBP1, MUTYH, BRCA1and RECQL4. In the whole cohort, somatic variants were found in 38 patients, with the following frequencies: TP53(N=7, 9.7%), ASXL1(N=7, 9.7%), SETBP1(N=5, 6.9%), NF1(N=5, 6.9%), SRSF2(N=4, 5.5%). Conclusion:In this subset of young adults with de novo MDS without congenital anomalies and/or familial history suggesting the presence of an undiagnosed congenital syndrome, 18% of the cohort harbored a likely causative germline variant. In addition, we noted a predominance of variants affecting genes with a cancer predisposition limited to the hematopoietic system, rather than classical telomere, DNA damage genes with an established mendelian link. Table. Table. Disclosures Díez-Campelo: Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Beschreibung: Myelodysplastic syndromes (MDS) and chronic myelomonocytic leukemia (CMML) are hematological disorders at high risk of progression to acute myeloid leukemia (sAML). Previous high-throughput sequencing studies have provided insight into the mutational dynamics and clonal evolution underlying disease progression. However, large serial sequencing studies are still required to define which type of mutations alone or in combination contribute to leukemic transformation. To assess the mutational profiles and mutational dynamics underlying progression from MDS to sAML, a targeted-deep sequencing (TDS) of 117 MDS/AML related-genes was performed in 110 bone marrow serial samples from 50 MDS/CMML patients who evolved to sAML and 5 patients who did not evolved (controls), at two different time-points: at the time of diagnosis and at sAML progression or after a median of 3 year follow-up, respectively. A total of 269 mutations in 57 different genes were identified at second sampling. At diagnosis, all patients, progressing and not progressing (controls), presented similar number of mutations (p=0.15). Moreover, patients evolving to sAML were then divided by FAB/WHO subtypes at diagnosis (CMML, low-risk and high-risk MDS subgroups) and no differences were observed in the number of mutations (p=0.71) and variant allele frequency (VAF) between each group (p=0.63). It should be noted that mutations in the splicing pathway were significantly more frequent in low-risk MDS patients (89% low-risk MDS vs. 56% high risk MDS, p=0.038). However, after progression, those patients who evolved to sAML displayed a statistically significant increase of mutations (p=0.001) at the leukemic phase, while controls did not at the follow-up sample (p=0.88). This higher number of mutations at second sampling in patients who evolved to sAML, independently of their diagnostic subtype, may be indicative of a higher genomic instability during disease evolution. To study the mutational dynamics and what mutations could be important during disease evolution, the VAFs of mutations detected at both time-points in each patient of transformation cohort were compared. We observed that some mutations identified at the sAML stage (163 mutations) were already present at the MDS stage, at clonal or subclonal levels, and were retained during evolution, for example in genes such as SRSF2 and DNMT3A. However, 106 mutations increased in clonal size or were newly acquired. Interestingly, most of mutations in Ras signaling pathway showed a same pattern: they were not present at time of diagnosis and appeared at sAML. In fact, mutations in this pathway were detected in 25 of 50 patients (50%) included in this cohort and in 22 of them (88%) mutations displayed this dynamic. Therefore, in this study, Ras signaling was the most common pathway involved in the progression from MDS to sAML. Of note, 9 of these patients (18% of the whole cohort) presented, independently of diagnosis, a co-occurring cohesin mutation, that was already present at diagnosis and, in most cases, markedly increased in clonal size at sAML. Thus, the combination of mutations in these two pathways could play an important role during disease evolution. In addition, 22 of 50 patients were treated with a disease-modifying agent (18 azacytidine and 4 lenalidomide) before they progressed to sAML, while the remaining 28 patients received no treatment or supportive care and were considered as non-treated. Thus, we studied the effect of disease-modifying therapy on mutational dynamics in this cohort of patients progressing to sAML. In the treated patients, a higher proportion of newly acquired or increasing mutations at sAML in chromatin modifiers was observed, while in non-treated patients most mutations remained stable (61% vs. 28.6%, p=0.013). By contrast, regarding treatment, no differences were detected in the mutational dynamics of cohesin (p=0.56) or Ras pathway (p=1.00). MDS progression to sAML was characterized by a higher genomic instability, independently of MDS subtypes of patients at diagnosis. Ras signaling was the most frequent affected pathway during disease evolution in this cohort and, interestingly, the co-occurrence of Ras signaling and cohesin mutations could play an important role in the progression. Moreover, mutations in chromatin modifiers genes could be related to the evolution of patients who received disease-modifying treatment before progression to sAML. Disclosures Olivier: Celgene: Honoraria; Jassen: Honoraria. Díez-Campelo:Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.

Beschreibung: Introduction Mesenchymal stem cells (MSC) are a key component of the hematopoietic niche. In the allogeneic hematopoietic stem cell transplantation (allo-HSCT) setting, the bone marrow stroma, and thus, their MSC remain of host origin. In a preliminary study we observed that, some patients at the early post allo-HSCT period, presented senescent bone marrow (BM) MSC, a finding that has not been previously described nor studied. The aims of our current study were: a) To multiparametrically characterize BM MSC at the early post allo-HSCT period (day +21). b) To confirm senescence of MSC and correlate with clinical and biological parameters (including biomarkers). c) To compare these cells with those from healthy donors. Methods We obtained BM samples on the day +21 post allo-HSCT from 136 patients. MSC were isolated, ex-vivo expanded and characterized, according to the criteria of the International Society for Cellular Therapy. We also obtained samples from peripheral blood at same day +21, for the study of biomarkers, which were analyzed by Luminex technique. The data were correlated with information from complete blood counts (CBC), and the morphological study of the bone marrow the same day. MSC from healthy donors were used as control. Results Patient baseline and transplant related characteristics are detailed in table 1. MSC were expanded ex-vivo showing normal growth, which were cryopreserved in passage 3 in the 33% (n=45/136) of the patients (Group-MSC-N). On the other hand, the remaining 67% (n=91/136), MSC showed premature signs of senescence, thus, not reaching to passage 1 (Group-MSC-S). Full BM chimerism on day+21 was seen in both groups (p=0.03). Concerning acute graft versus-host disease (aGVHD), in the Group-MSC-S, the incidence was 73% compared to 44% in the Group-MSC-N (p=0.001). The median time of the onset of aGVHD was 43 and 37 days respectively (p=0.04). The majority of cases presented with grades I-II in both groups. Plasma levels of biomarkers showed increased levels of Fas Ligand in the Group-MSC-S (p=0.009). There were no statistically significant differences regarding mortality nor relapse rates. Conclusions Bone marrow Mesenchymal stem cells may be severely damaged in some allo-HSCT recipients early after transplantation (day+21). This fact strongly correlates with the risk of development of acute GVHD. Disclosures Díez-Campelo: Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau.