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Myelodysplastic syndromes/neoplasms (MDS) are associated with variable clinical presentations and outcomes. The initial response criteria developed by the International Working Group (IWG) in 2000 have been used in clinical practice, clinical trials, regulatory reviews, and drug labels. While the IWG criteria were revised in 2006 and 2018 (the latter focusing on lower-risk disease), limitations persist in their application to higher-risk MDS and in their ability to fully capture clinical benefits of novel investigational drugs or to serve as valid surrogates for longer-term clinical endpoints (e.g., overall survival). Further, issues related to ambiguity and practicality of some criteria lead to variability in interpretation and inter-observer inconsistency in reporting results from the same sets of data. Thus, we convened an international panel of 36 MDS experts and used an established modified Delphi process to develop consensus recommendations for updated response criteria that would be more reflective of patient-centered and clinically relevant outcomes in higher-risk MDS. Among others, the IWG 2023 criteria include changes in the hemoglobin threshold for complete remission (CR), the introduction of CR with limited count recovery (CRL) and CR with partial hematologic recovery (CRh) as provisional response criteria, elimination of marrow CR, and specific recommendations for standardization of time-to-event endpoints and the derivation and reporting of responses. The updated criteria should lead to better correlation between patient-centered outcomes and clinical trial results in an era of multiple emerging new agents with novel mechanisms of action.

Background Patients with acute myeloid leukemia (AML) frequently harbor mutations in genes involved in the DNA (hydroxy)methylation pathway (DNMT3A, TET2, IDH1, and IDH2). In addition, changes in DNA methylation have been implicated in the pathogenesis of AML. Recently it was discovered that TET proteins are able to convert 5-methylcytosine into 5-hydroxymethylcytosine (5hmC), which is an important intermediate in the demethylation pathway. In this study, we measured 5-hydroxymethylcytosine levels in AML patients, and correlated these with mutational status and overall survival (OS). Patients and methods Samples from 206 clinically and molecularly well-characterized younger adult AML patients (≤60 years), included in the EORTC/GIMEMA AML-12 06991 clinical trial, were analyzed for mutations in DNMT3A, TET2, IDH1 and IDH2. 5-hydroxymethylcytosine levels were measured using HPLC-MS/MS. Results In healthy control cells, 5hmC levels were confined to a narrow range (1.5 fold difference), whereas in AML cells, a much wider range was detected (15 fold difference). In remission, 5hmC values were normalized to levels comparable to healthy bone marrow and peripheral blood, indicating that the aberrant 5hmC levels at diagnosis are intrinsic to the leukemic cells. Patients with mutations in TET2 and patients with mutations in IDH1/2 had significantly lower levels of 5hmC compared to patients without mutated TET2 and IDH1/2 (both P Conclusion Both low and very high levels of 5hmC are markers of poor prognosis in AML, lending further support for testing therapies targeting the DNA hydroxymethylation pathway. Disclosures: No relevant conflicts of interest to declare.

Background Outcome of patients with intermediate or high risk IPSS myelodysplastic syndrome (MDS) is poor in the absence of hematopoietic stem cell transplantation (HSCT). Choice of the best stem cell source is debated in this poor risk population. Unrelated cord blood transplantation (UCBT) has been used for patients lacking an HLA identical donor. This is the first study comparing well matched unrelated adult peripheral blood (PB) stem cell transplant to mismatched UCBT for patients with MDS. Method Patients with MDS transplanted from 2005 to 2011 with either unrelated CB or PB receiving a reduced intensity conditioning (RIC) were included. All PB donors were Human Leucocyte Antigens (HLA)-allele matched (10/10) or one allele mismatched (9/10) (-A, -B, -C, DRB1, -DQB1). Overall survival (OS) and disease-free survival (DFS) were estimated by Kaplan-Meier. Relapse incidence (RI), non-relapse mortality (NRM), engraftment, acute and chronic graft-versus-host disease (GVHD) were calculated using cumulative incidence (CInc) methods. Risk factors for outcomes were analyzed by Cox and Fine & Gray models. Results 502 patients transplanted with PB or 129 with CB (80 with double units) were compared. Among the PB recipients, 363 (72%) were 10/10 matched and 123 (25%) 9/10 matched. Most CB (98%) recipients had at least one HLA mismatch on 6 antigens tested (-A, -B antigen level and DRB1 allelic level), 32% had one mismatch and 66% had 2 mismatches. Median follow-up was 12 months for PB and 24 months for CB. MDS was transformed into AML in 416 patients. MDS WHO classification was: RA in 37, RCMD in 31, RAEB1 in 50 and RAEB2 in 87 and unclassified in 10 patients. Considering only patients with MDS, cytogenetic according to IPSS was: good in 96, intermediate in 57 and poor in 65 patients. PB and CB groups were different for age, gender, incidence of secondary AML (CB: 71% vs PB: 64%) and conditioning regimen. CInc of engraftment was lower in CB patients, 78 vs 96% (p The analyses were performed using 3 groups of patients according to donor HLA type: PB 10/10, PB 9/10 and CB. The unadjusted 2-year OS and DFS were better with PB 10/10 than with PB 9/10 or CB: 49%, 37% and 30% (p=0.0001) and 45%, 36%, 28% (p Conclusion Despite the limitation of a retrospective registry based study and the short term follow up, our study shows that transplants with PB from matched unrelated donor gives the best outcomes. In the absence of a 10/10 unrelated matched PB donor, a 9/10 PB donor or mismatched CB give similar results. Therefore, for MDS patients without a HLA 10/10 unrelated donor a 9/10 regardless of the specificity of the locus where the mismatch occurs mismatched HLA locus or a HLA mismatched CB are both alternative options for transplantation. Disclosures: Gluckman: Cord use: Honoraria; gamida: Honoraria.