Abstract: Core-binding factor (CBF) acute myeloid leukemia (AML) encompasses AML with inv(16)(p13.1q22) and AML with t(8;21)(q22;q22.1). Despite sharing a common pathogenic mechanism involving rearrangements of the CBF transcriptional complex, there is growing evidence for considerable genotypic heterogeneity. We comprehensively characterized the mutational landscape of 350 adult CBF-AML [inv(16): n = 160, t(8;21): n = 190] performing targeted sequencing of 230 myeloid cancer-associated genes. Apart from common mutations in signaling genes, mainly NRAS, KIT, and FLT3, both CBF-AML entities demonstrated a remarkably diverse pattern with respect to the underlying cooperating molecular events, in particular in genes encoding for epigenetic modifiers and the cohesin complex. In addition, recurrent mutations in novel collaborating candidate genes such as SRCAP (5% overall) and DNM2 (6% of t(8;21) AML) were identified. Moreover, aberrations altering transcription and differentiation occurred at earlier leukemic stages and preceded mutations impairing proliferation. Lasso-penalized models revealed an inferior prognosis for t(8;21) AML, trisomy 8, as well as FLT3 and KIT exon 17 mutations, whereas NRAS and WT1 mutations conferred superior prognosis. Interestingly, clonal heterogeneity was associated with a favorable prognosis. When entering mutations by functional groups in the model, mutations in genes of the methylation group (ie, DNMT3A, TET2) had a strong negative prognostic impact.

Abstract: Background: Acute myeloid leukemias (AML) with rearrangements of core-binding factor (CBF) complex genes (CBF-AML), comprising t(8;21) and inv(16) subgroups, are considered as diseases with favorable outcome. Nevertheless, CBF-AML relapse rates remain high, with ~40% of patients (pts) relapsing after standard intensive chemotherapy. Aim: To dissect the biology of relapse in CBF-AML, we performed whole exome sequencing (WES) in a large cohort of 101 cases at the time of diagnosis and for 47 cases also at the time of relapse. Methods: All pts were treated either with standard chemotherapy or with standard chemotherapy and kinase inhibitor dasatinib within clinical trials of the German-Austrian AML Study Group (AMLSG). Using the Nextera Rapid Capture Exome kit (Illumina) we performed WES of paired diagnostic (dx), remission and relapse samples of 47 pts, namely 21 pts with t(8;21) and 26 pts with inv(16). RNAseq was performed in 18 of these pts using the Ribo Zero RNA-sequencing kit (Illumina). To better define genomic signatures related to CBF-AML relapse, we included WES data previously published by our group (Faber et al. Nat Genet 2016). This set comprised dx samples of 8 t(8;21) and 10 inv(16) pts who relapsed as well as a control group of 20 t(8;21) and 16 inv(16) CBF-AML pts, who did not experience relapse. Results: For the new cohort, WES sequencing of 47 pts was performed with a mean coverage of 127-fold. In t(8;21), we identified a median of 3.5 mutations exclusively present at dx (range: 0-8), 11.6 mutations persistent from dx to relapse (range: 4-19), and 4.0 mutations gained at relapse (range: 2-7). For the inv(16) subgroup a median of 2.0 mutations were dx specific (0-7), 6.0 mutations persisted during tumor evolution (3-26) and 2.5 were gained at relapse (0-9). As previously reported, the spectrum of genes affected by mutations showed little overlap between t(8;21) and inv(16), except for commonly affected 'signaling' genes such as KIT, RAS, FLT3 and epigenetic players such as TET2. In total, in t(8;21) we identified 94 relapse-specific mutations or mutations displaying a strong increase in variant allele frequency (VAF) at relapse, and 63 of such relapse-specific alterations in inv(16) pts. In addition to the previously reported RUNX1 and cohesin complex gene mutations showing an increase in VAF at relapse, we found recurrent novel relapse-specific mutations in LAMC3, which occurred exclusively in the t(8;21) subgroup affecting 9% of pts. In inv(16), recurrent mutations in the tumor suppressor gene WT1 occurred in 12% of pts, either acquired at relapse or already present at dx as a minor subclone. Remarkably, mutations in relapsed t(8;21) pts often affected genes involved in PI3K-AKT and in cell cycle regulation pathways. In the inv(16) relapse group, in addition to dysregulation of the MAPK signaling pathway, we found several non-recurrent mutations in genes involved in ribosomal RNA metabolism, like in PRNAD1. Conclusion: Our WES sequencing results already provide first insights into the molecular composition and mechanisms underlying relapse in CBF-AML which often affect pathways linked to proliferation, such as PI3K-AKT and MAPK signaling. While we are currently validating additional hits, updated results will be provided at the ASH meeting, which will also address combinatorial mutation patterns underlying chemotherapy resistance in t(8;21) and inv(16) positive AML. Disclosures Götze: Celgene: Research Funding. Fiedler:Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding; Novartis: Consultancy, Honoraria; ARIAD/Incyte: Consultancy, Honoraria; Amgen: Consultancy, Honoraria, Other: support for meeting attendance, Patents & Royalties, Research Funding; Daiichi Sankyo: Other: support for meeting attendance; Gilead: Other: support for meeting attendance; Jazz Pharmaceuticals: Honoraria, Other: support for meeting attendance; Abbvie: Membership on an entity's Board of Directors or advisory committees; Morphosys: Consultancy, Honoraria; Celgene: Membership on an entity's Board of Directors or advisory committees. Thol:Celgene: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees. Heuser:PriME Oncology: Honoraria; Abbvie: Consultancy; Stemline Therapeutics: Consultancy; Karyopharm: Research Funding; Roche: Research Funding; Bayer: Consultancy, Research Funding; Amgen: Research Funding; BerGenBio ASA: Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Janssen: Consultancy; Daiichi Sankyo: Consultancy, Research Funding; Astellas: Research Funding. Ganser:Novartis: Consultancy; Celgene: Consultancy. Paschka:Agios Pharmaceuticals: Consultancy, Speakers Bureau; Astex Pharmaceuticals: Consultancy; Astellas Pharma: Consultancy, Speakers Bureau; Celgene: Consultancy, Other: Travel, accommodations or expenses; Jazz Pharmaceuticals: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Otsuka: Consultancy; Pfizer: Consultancy, Speakers Bureau; Sunesis Pharmaceuticals: Consultancy; AbbVie: Other: Travel, accommodation or expenses, Speakers Bureau; Amgen: Other; Janssen Oncology: Other; BerGenBio ASA: Research Funding. Döhner:GEMoaB: Consultancy, Honoraria; AROG: Research Funding; Astellas: Consultancy, Honoraria, Research Funding; Novartis: Consultancy, Honoraria, Research Funding; Helsinn: Consultancy, Honoraria; Jazz: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding; Astex: Consultancy, Honoraria; Roche: Consultancy, Honoraria; Pfizer: Research Funding; Oxford Biomedicals: Consultancy, Honoraria; Amgen: Consultancy, Honoraria, Research Funding; Agios: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria; AstraZeneca: Consultancy, Honoraria; Sunesis: Research Funding. Döhner:Novartis: Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Daiichi Sankyo: Honoraria; Abbvie: Consultancy; Sunesis Pharmaceuticals: Research Funding; Pfizer: Research Funding; Bristol-Myers Squibb: Research Funding; Jazz Pharmaceuticals: Consultancy, Honoraria, Research Funding; Astex Pharmaceuticals: Consultancy; Astellas Pharma: Consultancy; Amgen: Consultancy, Research Funding; Agios: Consultancy; Roche: Consultancy; Arog: Research Funding. Bullinger:Amgen: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Hexal: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Menarini: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees.

Abstract: MRD assessment in t(8;21) AML allows identification of patients at high relapse risk at defined time points during treatment and follow-up. MRD− after treatment is the most favorable factor for relapse risk and survival, and serial MRD analyses define cutoffs predicting relapse.

Abstract: Monitoring of measurable residual disease (MRD) provides prognostic information in patients with Nucleophosmin1-mutated (NPM1mut) acute myeloid leukemia (AML) and represents a powerful tool to evaluate treatment effects within clinical trials. We determined NPM1mut transcript levels (TLs) by quantitative reverse-transcription polymerase chain reaction and evaluated the prognostic impact of NPM1mut MRD and the effect of gemtuzumab ozogamicin (GO) on NPM1mut TLs and the cumulative incidence of relapse (CIR) in patients with NPM1mut AML enrolled in the randomized phase 3 AMLSG 09-09 trial. A total of 3733 bone marrow (BM) samples and 3793 peripheral blood (PB) samples from 469 patients were analyzed. NPM1mut TL log10 reduction ≥ 3 and achievement of MRD negativity in BM and PB were significantly associated with a lower CIR rate, after 2 treatment cycles and at end of treatment (EOT). In multivariate analyses, MRD positivity was consistently revealed to be a poor prognostic factor in BM and PB. With regard to treatment effect, the median NPM1mut TLs were significantly lower in the GO-Arm across all treatment cycles, resulting in a significantly greater proportion of patients achieving MRD negativity at EOT (56% vs 41%; P = .01). The better reduction in NPM1mut TLs after 2 treatment cycles in MRD positive patients by the addition of GO led to a significantly lower CIR rate (4-year CIR, 29.3% vs 45.7%, P = .009). In conclusion, the addition of GO to intensive chemotherapy in NPM1mut AML resulted in a significantly better reduction in NPM1mut TLs across all treatment cycles, leading to a significantly lower relapse rate.

Abstract: Background: FLT3-ITD occurs in ~25% of adult AML patients (pts) and is associated with poor prognosis. MRD monitoring is of high prognostic relevance, but restricted to certain AML subtypes. FLT3-ITD represents an attractive target for MRD monitoring in particular in pts treated with a tyrosine kinase inhibitor. FLT3-ITD MRD monitoring is hampered by the broad heterogeneity of ITD length and insertion site (IS). NGS may overcome these limitations offering the opportunity for MRD monitoring in FLT3-ITD+ AML. Aims: To validate our recently established NGS-based FLT3-ITD MRD assay in a defined cohort of FLT3-ITD+ AML pts treated within the AMLSG16-10 trial (NCT01477606) combining intensive chemotherapy with midostaurin followed by midostaurin maintenance and to evaluate the prognostic impact of FLT3-ITD MRD monitoring. Methods: Using FLT3-ITD paired-end NGS (Illumina MiSeq) with a variant allele frequency (VAF) sensitivity of 10-4-10-5 (Blätte et al., Leukemia 2019), 227 bone marrow (BM) and 17 peripheral blood samples from 61 FLT3-ITD+ AML pts were analyzed at diagnosis (Dx), after two cycles of chemotherapy (Cy2), at the end of treatment (EOT), and during 3-6 months follow-up (FU). All pts achieved complete remission (CR) after Cy2. Allogeneic hematopoietic cell transplantation in first CR was performed in 40 (66%) pts. Mutational status for NPM1 and DNMT3A was available for all pts (NPM1mut, n=48; DNMT3Amut, n=33; NPM1mut/DNMT3Amut, n=31), and NPM1mut MRD data for 41 pts. Results: At Dx we identified 191 ITDs; median length was 45 nucleotides (range, 9-194) and median VAF 0.279% (range, 0.006-90.21). Of the 191 ITDs, 133 (70%) located in the juxtamembrane domain (JMD) and 58 (30%) in the tyrosine kinase domain-1 (TKD1). There was no correlation of VAF with length or IS, whereas ITD size correlated with IS: the more C-terminal the IS, the longer the ITD (Rho=0.51; p & lt;.001). Total ITD VAF per pt was in median 34.3% (range, 0.007-90.21) and correlated positively with white blood cell count (WBC, Rho=0.314; p=.021) and lactate dehydrogenase serum level (LDH, Rho=0.274; p=.04), and inversely with the number of ITDs (Rho=-0.265; p=.04). Most pts (67%) exhibited & gt;1 ITD at Dx (median 2; range, 1-16). Categorizing pts according to IS as JMDsole (46%), JMD/TKD1 (34%), and TKD1sole (20%) revealed that JMD/TKD1 pts exhibited more ITD subclones (p & lt;.001) and a lower total VAF at Dx (p=.03). There were no correlations with any other clinical or genetic features. Pts' total ITD VAF significantly decreased after Cy2 and at EOT (median log10 reduction: 4.4 and 4.7; p & lt;.001, each), and MRD negativity (MRD-) was achieved in 67% and 87% of pts, respectively. According to subgroups, pts with JMDsole or TKD1sole showed deeper MRD reduction compared to JMD/TKD1 pts after Cy2 (4.6 vs 4.7 vs 3.7 log10; p=.06) and at EOT (4.8 vs 4.8 vs 4.0 log10; p=.02) but this did not result in a significant difference in achievement of MRD-. Concurrent NPM1mut was of favorable impact for log10 VAF reduction (median, 4.7 for DNMT3Amut/NPM1mut vs 4.6 for NPM1mut vs 2.8 others; p=.003) and MRD- (77 vs 76 vs 31%; p=.01) after Cy2, but exerted no impact at EOT. Correlating NPM1mut and FLT3-ITD MRD course revealed a positive correlation after Cy2 (Rho=0.327; p=.03), but not at EOT (Rho=0.250; p=.10), likely due to the higher sensitivity of the real-time quantitative PCR-based NPM1mut MRD assay. Median follow-up was 3.4 years (95% CI, 2.6-4.6). Survival analyses with respect to cumulative incidence of relapse (CIR; n=60) and overall survival (OS; n=61) revealed significantly lower CIR for total VAF at Dx & gt;34.3% (p=.03), a VAF reduction & gt;4.7 log10 (MR4.7) at EOT (p=.001), and for MRD- pts at EOT (p=.001). There was no impact on OS. In preliminary exploratory Cox regression (n=48), including BM blasts, WBC, LDH, age, and NPM1mut as covariables, MRD- at EOT was the only consistent favorable variable for CIR (HR, 0.1; p=.001) and OS (HR, 0.27; p=.03). During FU, 5/8 (63%) MRD+ pts at EOT became MRD- and 4/53 (8%) MRD- pts converted to MRD+ resulting in consecutive relapse in 2 pts. Conclusion: In this first cohort of FLT3-ITD+ AML pts treated with intensive chemotherapy and midostaurin in the prospective AMLSG16-10 trial we could demonstrate that FLT3-ITD NGS-based MRD monitoring is feasible and represents a promising tool to evaluate therapy response and identification of pts at a higher risk of relapse. Further analysis of the study cohort is ongoing. Disclosures Kapp-Schwoerer: Jazz Pharmaceuticals: Honoraria, Research Funding. Paschka:Sunesis Pharmaceuticals: Consultancy; BerGenBio ASA: Research Funding; Novartis: Consultancy, Speakers Bureau; Otsuka: Consultancy; Pfizer: Consultancy, Speakers Bureau; Astellas Pharma: Consultancy, Speakers Bureau; Celgene: Consultancy, Other: Travel, accommodations or expenses; Astex Pharmaceuticals: Consultancy; Jazz Pharmaceuticals: Consultancy, Speakers Bureau; Agios Pharmaceuticals: Consultancy, Speakers Bureau; Amgen: Other; Janssen Oncology: Other; AbbVie: Other: Travel, accommodation or expenses, Speakers Bureau. Fiedler:Ariad/Incyte: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Jazz Pharmaceuticals: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accomodations; Novartis: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: support in medical writing; Daiichi Sankyo Oncology: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accomodations; Morphosys: Membership on an entity's Board of Directors or advisory committees; BMS: Honoraria; AbbVie: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: support in medical writing; Servier: Honoraria, Other; BerGenBio ASA: Research Funding; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees, Other: travel accomodations, support in medical writing, Research Funding; Gilead: Honoraria. Salih:Novartis: Consultancy; Pfizer: Consultancy; Philogen: Consultancy; Medigene: Consultancy; Synimmune: Consultancy, Research Funding. Salwender:Bristol-Myers Squibb/Celgene: Honoraria; Janssen-Cilag: Honoraria; Amgen: Honoraria; Takeda: Honoraria; Oncopeptides: Honoraria; Sanofi: Honoraria; GlaxoSmithKline: Honoraria; AbbVie: Honoraria. Götze:Celgene: Research Funding. Luebbert:Janssen: Research Funding. Schlenk:PharmaMar: Research Funding; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees, Other: Travel, Accomodations, Expenses, Research Funding, Speakers Bureau; Novartis: Speakers Bureau; Roche: Research Funding; AstraZeneca: Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. Thol:Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Heuser:Daiichi Sankyo: Consultancy, Research Funding; Pfizer: Consultancy, Honoraria, Research Funding; Karyopharm: Research Funding; Abbvie: Consultancy; PriME Oncology: Honoraria; Amgen: Research Funding; Astellas: Research Funding; Roche: Research Funding; Stemline Therapeutics: Consultancy; Novartis: Consultancy, Honoraria, Research Funding; Janssen: Consultancy; BerGenBio ASA: Research Funding; Bayer: Consultancy, Research Funding. Ganser:Novartis: Consultancy; Celgene: Consultancy. Döhner:AstraZeneca: Consultancy, Honoraria; Sunesis: Research Funding; Roche: Consultancy, Honoraria; Pfizer: Research Funding; Oxford Biomedicals: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; Helsinn: Consultancy, Honoraria; Jazz: Consultancy, Honoraria, Research Funding; Janssen: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Bristol Myers Squibb: Consultancy, Honoraria, Research Funding; Astex: Consultancy, Honoraria; Astellas: Consultancy, Honoraria, Research Funding; AROG: Research Funding; Amgen: Consultancy, Honoraria, Research Funding; Agios: Consultancy, Honoraria, Research Funding; Abbvie: Consultancy, Honoraria; GEMoaB: Consultancy, Honoraria. Bullinger:Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees; Menarini: Membership on an entity's Board of Directors or advisory committees; Pfizer: Membership on an entity's Board of Directors or advisory committees; Novartis: Membership on an entity's Board of Directors or advisory committees; Abbvie: Membership on an entity's Board of Directors or advisory committees; Astellas: Membership on an entity's Board of Directors or advisory committees; Bristol-Myers Squibb: Membership on an entity's Board of Directors or advisory committees; Gilead: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Amgen: Membership on an entity's Board of Directors or advisory committees; Sanofi: Membership on an entity's Board of Directors or advisory committees; Hexal: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees. Döhner:Jazz Pharmaceuticals: Consultancy, Honoraria, Research Funding; Daiichi Sankyo: Honoraria; Celgene: Consultancy, Honoraria; Sunesis Pharmaceuticals: Research Funding; Novartis: Honoraria, Research Funding; Pfizer: Research Funding; Bristol-Myers Squibb: Research Funding; Arog: Research Funding; Roche: Consultancy; Astex Pharmaceuticals: Consultancy; Janssen: Consultancy, Honoraria; Amgen: Consultancy, Research Funding; Astellas Pharma: Consultancy; Agios: Consultancy; Abbvie: Consultancy.

Abstract: Background: Acute myeloid leukemia (AML) with t(8;21)(q22;q22.1) resulting in the RUNX1-RUNX1T1 gene fusion is considered favorable in the 2017 genetic risk stratification by the European LeukemiaNet (ELN). After intensive chemotherapy most patients (pts) achieve complete remission (CR), but relapse occurs in about 50% and is associated with poor prognosis. In this AML subgroup monitoring of measurable residual disease (MRD) has been shown to identify pts at higher risk of relapse. Aims: To assess the prognostic impact of MRD monitoring in bone marrow (BM) and peripheral blood (PB) in a large cohort of 155 clinically well-annotated t(8;21)-AML pts enrolled in one of six AMLSG treatment trials. Methods: RT-qPCR was used to quantify RUNX1-RUNX1T1 transcript levels (TL) reported as normalized RUNX1-RUNX1T1 values per 106 transcripts of the housekeeping gene B2M. Samples were analyzed in triplicate, the sensitivity was up to 10-6. Results: While pretreatment RUNX1-RUNX1T1 TL did not impact prognosis, both reduction of RUNX1-RUNX1T1 TL and achievement of MRD negativity (MRDneg) at end of treatment (EOT) were of significant prognostic importance in BM as well as in PB: MR2.5 ( 〉 2.5 log reduction) after treatment cycle 1 and MR3.0 after cycle 2 were significantly associated with a reduced relapse risk (MR2.5, BM: P=.034; PB: P=.008 and MR3.0, BM: P=.028; PB: P=.036, respectively). After completion of therapy, MRDneg was an independent favorable prognostic factor for cumulative incidence of relapse (CIR) (4-year CIR BM: 17% vs 36%, P=.021; PB: 23% vs 55%; P=.001) and overall survival (OS) (4-year OS rate BM: 93% vs 70%, P=.007; PB: 87% vs 47%; P 〈 .0001). Moreover, maximally selected Gray´s statistic defined specific MRD cut-offs at EOT associated with a lower relapse risk: 〈 83 RUNX1-RUNX1T1 TL in BM and 〈 5 in PB predicted for superior 4-year CIR (BM: 18% vs 61%; P 〈 .0001; PB: 23% vs 65%; P 〈 .0001). During follow-up serial MRD analyses allowed prediction of relapse in 77% of pts exceeding an arbitrary cut-off of 150 RUNX1-RUNX1T1 TL in BM and in 84% of pts with 〉 50 TL in PB, respectively. KIT mutation observed in 28% of pts predicted for lower CR rate and inferior outcome, but its prognostic impact was outweighed by RUNX1-RUNX1T1 TL during treatment. To determine whether PB could provide similar prognostic information as BM, we compared 680 paired samples (diagnosis, n=125; after cycle 1, n=80; after cycle 2, n=86; at EOT, n=78; during follow-up, n=311). At diagnosis RUNX1-RUNX1T1 TL tended to be slightly higher in BM than in PB (P=.072), but were significantly higher after cycle 1 (P=.008), cycle 2 (P 〈 .001), at EOT (P=.002), and during follow-up (P 〈 .001). RUNX1-RUNX1T1 TL in BM and PB correlated well (r=.87; P 〈 .0001) with on average 1-log lower values in PB. However, 2.5%, 26.7%, 26.9%, and 24.8% of all pairs were discrepant (BMpos/PBneg or BMneg/PBpos) after cycle 1, cycle 2, at EOT, and during follow-up. Of 104 PBneg samples obtained during treatment, 46 (44%) were still BMpos. In the post-treatment period, this fraction decreased to 28% (77 BMpos/276 PBneg pairs) (P=.003). Of note, RUNX1-RUNX1T1 TL in all but four of the 77 (5.2%) BMpos samples were below the cut-off of 150 TL. Virtually all relapses occurred within one year after EOT with a very short latency from molecular to morphologic relapse strongly suggesting to perform MRD assessment at short intervals during this period. Based on our data we refined the practical guidelines for MRD assessment in RUNX1-RUNX1T1-positive AML: i) along with the current ELN MRD recommendations, BM and PB should be analyzed after each treatment cycle; ii) during the follow-up period, in particular the first year after EOT, MRD monitoring in PB should be performed monthly; in pts with TL 〉 50 in PB, increase of MRD TL 〉 1-log, and/or conversion from MRDneg to MRDpos a complementary BM samples should be analyzed timely. Summary: RUNX1-RUNX1T1 MRD monitoring allows for the discrimination of pts at high and low risk of relapse. MRDneg in both BM and PB after completion of therapy was the most valuable independent favorable prognostic factor for relapse risk and OS. During follow-up, serial MRD analyses allowed the definition of cut-offs predicting relapse. Moreover, considering that virtually all relapses occurred within the first year after EOT with a very short latency from molecular to morphologic relapse MRD assessment in PB at shorter intervals during this period is indispensable. Disclosures Weber: Celgene Corporation: Research Funding. Schroeder:Celgene Corporation: Consultancy, Honoraria, Research Funding. Götze:AbbVie: Membership on an entity's Board of Directors or advisory committees. Fiedler:Amgen, Pfizer, Abbvie: Other: Support in medical writing; Amgen, Pfizer, Novartis, Jazz Pharmaceuticals, Ariad/Incyte: Membership on an entity's Board of Directors or advisory committees; Amgen: Research Funding; Amgen, Jazz Pharmaceuticals, Daiichi Sanchyo Oncology, Servier: Other: Support for meeting attendance. Greil:Gilead: Consultancy, Honoraria, Other: Travel/accomodation expenses, Research Funding; MSD: Consultancy, Honoraria, Other: Travel/accomodation expenses, Research Funding; Takeda: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria, Research Funding; Daiichi Sankyo: Consultancy, Honoraria; Sandoz: Honoraria. Krauter:Pfizer: Honoraria. Bullinger:Amgen: Honoraria; Astellas: Honoraria; Gilead: Honoraria; Daiichi Sankyo: Honoraria; Hexal: Honoraria; Janssen: Honoraria; Jazz Pharmaceuticals: Honoraria; Menarini: Honoraria; Novartis: Honoraria; Pfizer: Honoraria; Abbvie: Honoraria; Bayer: Other: Financing of scientific research; Sanofi: Honoraria; Seattle Genetics: Honoraria; Bristol-Myers Squibb: Honoraria; Celgene: Honoraria. Paschka:Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Travel expenses, Speakers Bureau; Jazz: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; BMS: Other: Travel expenses, Speakers Bureau; Agios: Membership on an entity's Board of Directors or advisory committees; Amgen: Other: Travel expenses; Otsuka: Membership on an entity's Board of Directors or advisory committees; Takeda: Other: Travel expenses; Janssen: Other: Travel expenses; Abbvie: Other: Travel expenses; Sunesis: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees, Other: Travel expenses, Speakers Bureau; Astex: Membership on an entity's Board of Directors or advisory committees, Travel expenses; Astellas: Membership on an entity's Board of Directors or advisory committees. Döhner:AbbVie, Agios, Amgen, Astellas, Astex, Celator, Janssen, Jazz, Seattle Genetics: Consultancy, Honoraria; Celgene, Novartis, Sunesis: Honoraria, Research Funding; AROG, Bristol Myers Squibb, Pfizer: Research Funding. Döhner:Celgene: Honoraria; Janssen: Honoraria; CTI Biopharma: Consultancy, Honoraria; Daiichi: Honoraria; Jazz: Honoraria; Novartis: Honoraria.