ALBERT

Description: 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 (TL) by RQ-PCR and evaluated the prognostic impact of NPM1mut MRD and the effect of gemtuzumab ozogamicin (GO) on NPM1mut TL and the cumulative incidence of relapse (CIR) in patients with NPM1mut AML enrolled in the randomized phase III AMLSG 09-09 trial. 3733 bone marrow (BM) 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 two treatment cycles and at end of treatment (EOT). In multivariate analyses, MRD positivity consistently revealed as poor prognostic factor in BM and PB. With regard to treatment effect, the median NPM1mut TL were significantly lower in the GO-Arm across all treatment cycles, resulting in a significantly higher proportion of patients achieving MRD negativity at EOT (56% vs 41%; P=.01). The betterreduction of NPM1mut TL after two 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 of NPM1mut TL across all treatment cycles leading to a significantly lower relapse rate. The AMLSG 09-09 trial was registered at www.clinicaltrials.gov as #NCT00893399.

Description: Background: CBF-AML is defined by recurrent genetic abnormalities which encompass t(8;21)(q22;q22), inv(16)(p13.1q22) or less frequently t(16;16)(p13.1;q22). Most frequent secondary chromosome aberrations in t(8;21) AML are del(9q) or loss of a sex chromosome, and in inv(16)/t(16;16) AML trisomy 22 or trisomy 8. At the molecular level mutations involving KIT, FLT3, or NRAS were identified as recurrent lesions in CBF-AML. However, the underlying genetic alterations which might trigger relapse in CBF-AML are not well delineated. Thus, the aim of our study was to characterize the clonal architecture of relapsed CBF-AML. Methods: We performed mutational profiling (KIT, FLT3-ITD, FLT3-TKD, NRAS, ASXL1) in paired samples obtained at diagnosis and at relapse from 66 adults with CBF-AML [inv(16), n=43; t(8;21), n=23] who all were treated within the AMLSG studies. Results: In inv(16) AML, the following mutation pattern was identified at diagnosis: KIT 13/40 (33%; exon 8, n=6; exon 17, n=5; exon 8+17, n=1; exon 11, n=1; missing data, n=3), NRAS 18/43 (42%), FLT3-TKD 4/43 (9%); none of the pts harboured FLT3-ITD or ASXL1 mutations. At the time of relapse, there was a shift in the mutation pattern in 26 pts (60%): KIT mutations (exon 8, n=5; exon 17, n=2; exon 8+17, n=1) were lost in 8 pts and 1 pt acquired an exon 17 KIT mutation; similarly, 15 pts lost and 1 pt gained NRAS mutation, respectively. Of note, all FLT3-TKD mutations were lost at the time of relapse, and only one pt gained a FLT3-ITD mutation. Based on these findings we calculated the stability in inv(16) AML for KIT, NRAS and FLT3-TKD mutations as 38%, 17%, and 0%, respectively. AML with t(8;21) presented a different diagnostic mutation profile: KIT 9/23 (39%; exon 17, n=8; exon 11, n=1), FLT3 -ITD 3/23 (13%), NRAS 2/23 (9%), and ASXL1 1/23 (4%); there were no FLT3-TKD mutations. At the time of relapse, the mutation pattern changed in 9 pts (39%); KIT mutations were lost in 4 pts (exon 17, n=3; exon 11, n=1), but acquired in 2 pts with both of them located in exon 17; only 1 pt lost the NRAS mutation. FLT3-ITD was lost in 2 and gained in 3 pts. There was no change in the ASXL1 mutation status. Thus, the stability for KIT, NRAS, FLT3-ITD and ASXL1 mutations in t(8;21) AML was calculated as 56%, 50%, 33% and 100%, respectively. Of note, mutations affecting the KIT and NRAS gene were almost mutually exclusive; there were only 3 pts with concurrent KIT and NRAS mutations at diagnosis [inv(16), n=2; t(8;21), n=1]. Conclusion: CBF-AML cases display a high degree of molecular heterogeneity with shift of the mutation pattern at relapse in both CBF-AML subtypes. The frequent loss of KIT and NRAS mutations at relapse suggests that there might be other important secondary lesions driving relapse. Ongoing high-resolution genome-wide profiling will further unravel the clonal hierarchy and genomic landscape in CBF-AML. Disclosures Götze: Novartis: Honoraria; Celgene Corp.: Honoraria. Greil:Celgene: Consultancy; Ratiopharm: Research Funding; Sanofi Aventis: Honoraria; Pfizer: Honoraria, Research Funding; Boehringer-Ingelheim: Honoraria; Astra-Zeneca: Honoraria; GSK: Research Funding; Novartis: Honoraria; Genentech: Honoraria, Research Funding; Janssen-Cilag: Honoraria; Merck: Honoraria; Mundipharma: Honoraria, Research Funding; Eisai: Honoraria; Amgen: Honoraria, Research Funding; Cephalon: Consultancy, Honoraria, Research Funding; Bristol-Myers-Squibb: Consultancy, Honoraria; AOP Orphan: Research Funding; Roche, Celgene: Honoraria, Research Funding. Schlenk:Boehringer-Ingelheim: Honoraria; Teva: Honoraria, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Research Funding; Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Research Funding; Arog: Honoraria, Research Funding.

Description: Background: In 2010 an international expert working group (European LeukemiaNet, ELN) has published recommendations for the diagnosis and management of acute myeloid leukemia (AML) including a risk stratification by cyto- and molecular genetics, subdividing AML into four risk groups. Emerging data on molecular markers in AML has led to an update of stratification criteria by ELN in 2017 including the recommendation for screening of the high-risk (HR) molecular markers ASXL1, RUNX1, and TP53 that have been shown to confer poor prognosis. The identification of HR markers results in a shift of the prognostic stratification towards adverse risk. Aim: To investigate the mutational landscape and to assess the prevalence of HR markers in patients (pts) with newly diagnosed AML classified as intermediate-I or -II risk (inter-I/-II) based on the 2010 ELN criteria in a prospective real-world application. Methods: Using a next-generation targeted sequencing approach [HaloPlex HS (Agilent) on a Miseq (Illumina)], we performed a prospective analysis of all coding regions of 42 target genes including the HR marker ASXL1, RUNX1, and TP53 in 329 newly diagnosed intermediate risk AML pts all enrolled in the AMLSG Biology and Outcome (BiO)-Registry [NCT01252485] of the German-Austrian AML Study Group (AMLSG). Pt genetic features obtained at diagnosis were as follows: inter-I: normal karyotype, n=198 (60%); inter-II: trisomy 8, n=28 (9%), nullisomy Y, n=12 (4%), t(9;11)(p21.3;q23.3), n=7 (2%), others, n=83 (25%); FLT3-internal tandem duplication (FLT3-ITD+), n=75 (23%), mutations (mut) in tyrosine kinase domain of FLT3 (FLT3-TKDmut), n=12 (3.6%), NPM1mut, n=59 (18%); median age was 67 years (range: 21-89 yrs); 60% of pts were male. Results: Overall, 1253 mut in 315 pts (96%) were identified. Mut in at least one of the HR markers were identified in 50% (n=166) of the pts. Mut in ASXL1 occurred in 32% (105/329), followed by RUNX1 in 26% (87/329), and TP53 in 4% (13/329) of the pts, respectively. Pts with mut in one of the three HR markers showed lower WBC (median 7.63 vs 24.25 109/L, P=.003), lower hemoglobin value (median 8.8 vs 9.3 g/dl, P=.01), lower LDH serum level (median 330 vs 559 U/l, P

Description: Introduction BRCA1/BRCA2-containing complex 3 (BRCC36) is a Lys63-specific deubiquitinating enzyme (DUB) involved in DNA damage repair. Mutations in BRCC36 have been identified in 2-3% of patients with myelodysplastic syndromes (MDS) and secondary AML (sAML). The role of BRCC36 mutations in de novo AML and their impact on DNA damage-inducing cytotoxic chemotherapy sensitivity is not clear. Aim We aimed to determine the incidence of BRCC36 mutations in AML and their impact on outcome and drug sensitivity in vitro. Methods We analyzed the entire coding region of BRCC36 for mutations in 191 AML cases with t(8;21) (q22;q22.1) and 95 cases with inv(16) (p13.1q22) using a customized targeted sequencing panel. Data for de novo AML was derived from The Cancer Genome Atlas Research Network (TCGA) data set (NEJM 2013). Lentiviral CRISPR/Cas9 was used to inactivate BRCC36 in t(8;21)-positive AML cell lines - Kasumi-1 and SKNO-1 - and murine hematopoietic stem and progenitor cells (LSKs). Knockout was confirmed by a cleavage assay as well as Western blot. AML1-ETO-9a was expressed by a retroviral vector. Cell lines and LSK cells were treated with different concentrations of doxorubicin or cytarabine and their viability was assessed seven days post treatment. DNA damage was assessed through phospho-γH2AX staining using flow-cytometry. Results BRCC36 mutations were identified in 7 out of 191 patients (3.7%) with t(8;21) AML and none of 95 patients with inv(16). In the TCGA data set one out of 200 patients (0.5%) with de novo AML had a BRCC36 mutation. This patient had a complex karyotype and would be considered as secondary AML with myelodysplastic-associated changes according to the 2016 WHO classification. Six of the 7 mutations were missense or nonsense mutations that were predicted to be deleterious to BRCC36 function. One mutation affected a splice site at exon 6, resulting in an impaired splicing capability. With intensive standard chemotherapy all patients with BRCC36 mutations achieved a complete remission and had an estimated relapse-free and overall survival of 100% after a median follow up of 4.2 years. Given its role in DNA damage repair, we hypothesized that BRCC36 inactivation sensitizes AML cells to DNA-damage inducing drugs. In order to test this, we generated BRCC36 knockout Kasumi-1 and SKNO-1 cell lines using CRISPR-Cas9. BRCC36 inactivation had no impact on cell growth on either of the cell lines. However, we found that BRCC36 knockout cells were significantly more sensitive to doxorubicin as compared to the parental cells with normal BRCC36. This was accompanied by a significant increase in DNA damage as assessed by phospho-γH2AX in BRCC36 knockout vs control cells after doxorubicin treatment. In contrast, BRCC36 inactivation had no impact on cytarabine sensitivity. We next assessed drug sensitivity in primary murine leukemic cells expressing AML1-ETO-9a. Again, inactivation of BRCC36 resulted in a significant higher sensitivity to doxorubicin but not cytarabine. Conclusion We found BRCC36 to be recurrently mutated in t(8;21)-positive AML Inactivation of BRCC36 was associated with impairment of the DNA damage repair pathway and thus higher sensitivity to DNA damage-inducing chemotherapy. This might be also reflected by the favorable clinical outcome of patients with BRCC36 mutated t(8;21)-positive AML, a finding which has to be confirmed in a large patient cohort. Disclosures Paschka: Pfizer: Membership on an entity's Board of Directors or advisory committees; Takeda: Other: Travel support; Novartis: Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Speakers Bureau; Otsuka: Membership on an entity's Board of Directors or advisory committees; Sunesis: Membership on an entity's Board of Directors or advisory committees; Jazz: Speakers Bureau; Amgen: Other: Travel support; Janssen: Other: Travel support; Bristol-Meyers Squibb: Other: Travel support, Speakers Bureau; Celgene: Membership on an entity's Board of Directors or advisory committees, Other: Travel support, Speakers Bureau; Astellas: Membership on an entity's Board of Directors or advisory committees, Travel support; Astex: Membership on an entity's Board of Directors or advisory committees; Agios: Membership on an entity's Board of Directors or advisory committees. Bullinger:Jazz Pharmaceuticals: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Speakers Bureau; Bayer Oncology: Research Funding; Sanofi: Research Funding, Speakers Bureau; Janssen: Speakers Bureau; Bristol-Myers Squibb: Speakers Bureau; Amgen: Honoraria, Speakers Bureau; Novartis: Honoraria, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Döhner:Novartis: Consultancy, Honoraria, Research Funding; Jazz: Consultancy, Honoraria; Jazz: Consultancy, Honoraria; AROG Pharmaceuticals: Research Funding; Janssen: Consultancy, Honoraria; Celator: Consultancy, Honoraria; Pfizer: Research Funding; Celgene: Consultancy, Honoraria, Research Funding; Astex Pharmaceuticals: Consultancy, Honoraria; AROG Pharmaceuticals: Research Funding; Janssen: Consultancy, Honoraria; Seattle Genetics: Consultancy, Honoraria; Sunesis: Consultancy, Honoraria, Research Funding; Astellas: Consultancy, Honoraria; Astex Pharmaceuticals: Consultancy, Honoraria; Bristol Myers Squibb: Research Funding; Pfizer: Research Funding; Agios: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Research Funding; AbbVie: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Amgen: Consultancy, Honoraria; Agios: Consultancy, Honoraria; AbbVie: Consultancy, Honoraria; Celator: Consultancy, Honoraria; Astellas: Consultancy, Honoraria; Bristol Myers Squibb: Research Funding; Seattle Genetics: Consultancy, Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Sunesis: Consultancy, Honoraria, Research Funding.

Description: 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

Description: Patients with acute myeloid leukemia (AML) harboring FLT3 internal tandem duplications (ITDs) have poor outcomes, in particular AML with a high (≥0.5) mutant/wild-type allelic ratio (AR). The 2017 European LeukemiaNet (ELN) recommendations defined 4 distinct FLT3-ITD genotypes based on the ITD AR and the NPM1 mutational status. In this retrospective exploratory study, we investigated the prognostic and predictive impact of the NPM1/FLT3-ITD genotypes categorized according to the 2017 ELN risk groups in patients randomized within the RATIFY trial, which evaluated the addition of midostaurin to standard chemotherapy. The 4 NPM1/FLT3-ITD genotypes differed significantly with regard to clinical and concurrent genetic features. Complete ELN risk categorization could be done in 318 of 549 trial patients with FLT3-ITD AML. Significant factors for response after 1 or 2 induction cycles were ELN risk group and white blood cell (WBC) counts; treatment with midostaurin had no influence. Overall survival (OS) differed significantly among ELN risk groups, with estimated 5-year OS probabilities of 0.63, 0.43, and 0.33 for favorable-, intermediate-, and adverse-risk groups, respectively (P 〈 .001). A multivariate Cox model for OS using allogeneic hematopoietic cell transplantation (HCT) in first complete remission as a time-dependent variable revealed treatment with midostaurin, allogeneic HCT, ELN favorable-risk group, and lower WBC counts as significant favorable factors. In this model, there was a consistent beneficial effect of midostaurin across ELN risk groups.

Description: Background: The ASXL2 (Additional Sex comb-like 2) gene on chromosome 2p23.3 encodes an epigenetic regulator that is thought to act through histone modification and thereby regulating gene transcription in a context-dependent manner. Recently, ASXL2 mutations (ASXL2mut) were found with a high incidence (~23%) in a cohort of 110 pediatric or adult AML patients (pts) with t(8;21)(q22;q22) (Micol et al., Blood 2014). Aim: We assessed the frequency and prognostic impact of ASXL2mut in the context of other clinical and genetic factors in a large clinically well-defined cohort of intensively treated adults with t(8;21) AML. In addition, the stability of ASXL2 mutation status was analysed in a subset of pts at the time of relapse. Methods: Diagnostic samples from 204 adults with t(8;21);RUNX1/RUNX1T1 -positive AML [median age: 49 years, range: 18-82] were analysed for ASXL2mut in exon 11 and 12 using a combination of PCR-based amplification and subsequent direct DNA-sequencing. Paired samples at diagnosis and relapse were evaluated for the ASXL2 mutation status in a subset of 22 pts. Additional mutation analyses were performed for KIT, FLT3 (ITD and TKD), NRAS, and ASXL1 genes. All pts received intensive treatment either within AMLSG trials (n=155) or according to standard chemotherapy regimens. Results: Thirty four ASXL2mut were identified in 33 (16.2%) of the 204 pts. All mutations (frame-shifts, n=32; non-sense, n=2) created stop codons leading to premature protein truncation with loss of the terminal PHD domain; 27% of the mutations affected codon T740 in exon 12. At diagnosis, there was no significant difference between pts with ASXL2mut and ASXL2 wildtype (ASXL2wt) with respect to sex, WBC, haemoglobin, platelets, LDH serum levels, and circulating or bone marrow blasts. Of note, ASXL2mut were not associated with increasing age, a finding which is commonly observed for ASXL1 mutations in AML. In terms of secondary chromosome aberrations ASXL2mut were frequently associated with del(9q) (P=.006), whereas they never co-occurred with trisomy 8. There was no significant association between ASXL2mut and all other gene mutations analysed. Analysis for ASXL2 mutation status in 22 paired samples obtained at diagnosis and relapse showed a high stability since the mutation was still present in two pts at relapse whereas none of the remaining 20 ASXL2 wildtype cases acquired ASXL2mut. There was no difference in complete remission (CR) rate after double induction between pts with ASXL2mut (88%) and those with ASXL2wt (92%); the same was true when comparing pts with ASXL1 or ASXL2 mutations (ASXL1/2mut) as one group (93%) versus those with ASXL1/2 wildtype. Neither ASXL2mut nor ASXL1/2mut did impact the endpoints event-free-survival, cumulative incidence of relapse, relapse-free and overall survival. Conclusions: Beside KIT and NRAS, ASXL2 is among the most frequently mutated genes in t(8;21) AML. ASXL2mut did not impact achievement of CR or any survival endpoint. Nevertheless, the high incidence (16.2%) of ASXL2mut in t(8;21) AML and the exclusivity to this subgroup of core-binding factor AML implies a peculiar role of ASXL2 in the leukemogenesis of t(8;21) AML providing a basis for further studies. Disclosures Horst: MSD: Research Funding; Pfizer: Research Funding; Amgen: Honoraria, Research Funding; Gilead: Honoraria, Research Funding; Boehringer Ingleheim: Research Funding. Schlenk:Daiichi Sankyo: Membership on an entity's Board of Directors or advisory committees; Novartis: Honoraria, Research Funding; Pfizer: Honoraria, Research Funding; Janssen: Membership on an entity's Board of Directors or advisory committees; Boehringer-Ingelheim: Honoraria; Arog: Honoraria, Research Funding; Teva: Honoraria, Research Funding.

Description: Key Points 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.

Description: Background: Approximately 5% of adult acute myeloid leukemia (AML) cases are associated with balanced translocations of chromosome 11q23, and AML with t(9;11)(p22;q23) is recognized as a distinct entity by the WHO Classification. Similarly, the presence of t(4;11)(q21;q23), which accounts for 8-10% of B-cell precursor acute lymphoblastic leukemia (ALL) in patients over the age of 20 years, defines a distinct entity termed "B-lymphoblastic leukemia with t(v;11q23)" according to the WHO Classification. On the molecular level, t(11q23) result in fusion of the KMT2A (also called MLL) gene, which encodes a histone 3 lysine 4 methyltransferase, to a broad spectrum of more than 70 partner genes. The prognosis of patients with relapsed/refractory KMT2A-rearranged leukemia is very poor, and new treatment approaches are needed. Using in vitro and in vivo experimental models, we previously identified cyclin dependent kinase 6 (CDK6) as a potential therapeutic target in KMT2A-rearranged leukemias (Placke et al. Blood. 2014;124:13-23). Aims: To evaluate the tolerability and efficacy of the small-molecule CDK4/6 inhibitor palbociclib in KMT2A-rearranged AML and ALL within a genotype-guided clinical trial (AMLSG 23-14; ClinicalTrials gov. Identifier NCT02310243). Methods: Patients with KMT2A-rearranged leukemia, either relapsed/refractory or newly diagnosed but ineligible for intensive chemotherapy, are enrolled. The study is a phase Ib/IIa trial with a safety/tolerability part in the phase Ib using the standard palbociclib dose of 125 mg once daily for 21 days in a 28-day cycle. Based on a 3+3 modified Fibonacci design, a dose deescalation to 100 mg and 75 mg in case of toxicity is possible in sequential cohorts. If no or only one limiting toxicity is observed among 6 patients at one dose level, this dose level will be taken forward to the phase IIa expansion part of the study. Limiting toxicities are defined as toxicities attributable to palbociclib, expected or unexpected. The expansion part of the study is based on Simon's optimal 2-stage design with 18 patients and 43 patients in the 2 stages. Results: The phase Ib of the study has been completed with recruitment of 6 patients with relapsed/refractory leukemia (AML, n=3; treatment-related AML, n=2; ALL, n=1; refractory to intensive chemotherapy, n=2; relapse, n=4 [following allogeneic stem cell transplantation, n=3; following chemotherapy, n=1]). Cytogenetic results were as follows: t(9;11), n=3; t(6;11), n=1; t(11;19), n=1; t(4;11), n=1. The median white blood cell count (WBC) at study inclusion was 7.05 G/l (range, 0.9-61.0). To control hyperleukocytosis, 3 patients were treated with hydroxyurea during the first week of palbociclib and one patient with corticosteroids. No limiting toxicity occurred during the first 28-day cycle, the limiting-toxicity assessment period. White blood cell counts rapidly decreased after one week of palbociclib at a dose of 125 mg/day and remained low until week 3 (median, 1.6 G/l; range, 0.6-1.9). The median WBC after one week of drug holiday was 1.9 G/l (range, 1.3-7.3). Response assessment revealed one partial remission, 3 disease stabilizations, and 2 cases of progressive disease. Four patients completed further treatment cycles (median, 2; range 2-6), with one patient achieving a complete remission with incomplete hematologic recovery after cycle 2. This patient, a 76-year-old man with t(11;19)-positive de novo AML refractory to chemotherapy with daunorubicin and cytarabine, relapsed after cycle 6, and correlative laboratory studies are underway to determine potential resistance mechanisms. Conclusions: Palbociclib is well tolerated in patients with refractory/relapsed KMT2A-rearranged leukemia with no occurrence of limiting toxicities and has clinical activity in this prognostically unfavorable subset of AML/ALL. Therefore, the study will be taken forward to the efficacy part with accrual of further patients. In addition, the protocol is currently amended as a basket trial with inclusion of patients with locally advanced/metastatic chordoma based on preclinical evidence that CDK4/6 dependence represents a specific liability of chordoma cells that could be exploited for therapeutic benefit. Disclosures Lübbert: Celgene: Other: Travel Funding; Ratiopharm: Other: Study drug valproic acid; Janssen-Cilag: Other: Travel Funding, Research Funding. Schlenk:Amgen: Research Funding; Pfizer: Honoraria, Research Funding.

Description: Background: Acute myeloid leukemia (AML) with t(8;21)(q22;q22) results in the formation of the RUNX1-RUNX1T1 fusion transcript which can be used to monitor minimal residual disease (MRD) by quantitative reverse transcriptase polymerase chain reaction (qRT-PCR). Early identification of patients (pts) with a high risk of relapse will allow pre-emptive therapy including allogeneic hematopoietic cell transplantation (alloHCT). Recent studies in AML with NPM1 mutation or the CBFB-MYH11 gene fusion revealed that MRD persistence is significantly associated with a high risk of relapse. However, the prognostic impact of MRD assessment in RUNX1-RUNX1T1-positive AML is not well established. Aims: To assess the prognostic impact of qRT-PCR-based MRD monitoring in bone marrow (BM) of pts with t(8;21)/RUNX1-RUNX1T1-positive AML obtained at defined time-points (diagnosis, first and second cycle of chemotherapy, end of treatment). Methods: In total, 120 pts were included based on the availability of a diagnostic BM sample and at least two subsequent BM samples obtained during therapy and at the end of treatment; 106 pts were enrolled in one of six AMLSG treatment trials: AML HD93 (n=1), AML HD98A (NCT00146120; n=13), AMLSG 06-04 (NCT00151255; n=4), AMLSG 07-04 (NCT00151242; n=43), AMLSG 11-08 (NCT00850382; n=31), AMLSG 21-13 (NCT02013648; n=14); 14 pts were treated outside clinical trials. All pts received anthracycline- and cytarabine-based intensive induction followed by subsequent high-dose cytarabine consolidation cycles. For MRD assessment, qRT-PCR from BM specimens was performed using TaqMan technology; RUNX1-RUNX1T1 transcript levels (TL) were reported as the normalized value of RUNX1-RUNX1T1 per 106 transcripts of the housekeeping gene beta2-microglobulin. The maximum sensitivity of the assay was 10-6. Results: The median age of the pts was 47 years (yrs; range, 18-73 yrs); at the time of diagnosis there was a broad range of RUNX1-RUNX1T1 TL (18490 to 14440000) with a median of 227800. RUNX1-RUNX1T1 TL did not correlate with clinical features (age, WBC, platelets, LDH, BM blasts) or associated gene mutations such as KIT, FLT3-ITD/TKD, NRAS or ASXL2. However, pts with additional FLT3 mutation showed higher TL compared to wild-type pts (median, 412955 vs 219052). Cox regression analysis using RUNX1-RUNX1T1 TL as a log10 transformed continuous variable showed that higher RUNX1-RUNX1T1 TL were significantly associated with a higher cumulative incidence of relapse (CIR), inferior event-free survival (EFS) and shorter overall survival (OS) for the two time points "after first treatment cycle" and "at end of treatment" (CIR: HR, 1.84, p=0.001; HR, 1.60, p=0.03; EFS: HR, 1.59, p=0.01, HR, 1.74, p=0.01; OS: HR, 1.63, p=0.02, HR 2.13, p=0.009, respectively). In univariate analyses achievement of MRD negativity (n=35) at the end of treatment was significantly associated with a superior 4-yr OS (93% vs 67%; p=0.007) and 4-yr EFS (81% vs 61%; p=0.04) whereas achievement of MRD negativity after the first (1/85) and second (20/89) treatment cycle was low not reaching significance for any of the clinical endpoints. Separation of the RUNX1-RUNX1T1 TL according to quartiles of distribution showed significant differences in OS (p=0.04), and remission duration (p=0.006) "after first cycle" whereas "at end of treatment" significant differences were only found for OS (p=0.009). Finally, we evaluated the impact of concurrent KIT mutations on the kinetics of RUNX1-RUNX1T1 TL. Following the first treatment cycle, the median RUNX1-RUNX1T1 TL were significantly lower in the KIT wildtype group compared with the KIT mutated group (p=0.02); the same was true "at the end of treatment" (p=0.02). Conclusions: In our study, achievement of MRD negativity at the end of treatment was significantly associated with a better outcome in t(8;21)-positive AML. The fact that earlier time points did not allow the identification of pts with a high relapse risk is probably due to the high sensitivity of the qRT-PCR assay which is also reflected by the low number of pts achieving qRT-PCR negativity after first and second treatment cycle, respectively. Further analyses are ongoing including multivariable as well as molecular subgroup analyses. *These authors contributed equally to the work: MA, AC MA was supported by the Else-Kröner-Fresenius-Stiftung (EKFS). Disclosures Paschka: Celgene: Honoraria; Pfizer Pharma GmbH: Honoraria; Bristol-Myers Squibb: Honoraria; Medupdate GmbH: Honoraria; Novartis: Consultancy; ASTEX Pharmaceuticals: Consultancy. Lübbert:Ratiopharm: Other: Study drug valproic acid; Janssen-Cilag: Other: Travel Funding, Research Funding; Celgene: Other: Travel Funding. Fiedler:Amgen: Consultancy, Other: Travel, Patents & Royalties, Research Funding; Teva: Other: Travel; Kolltan: Research Funding; Ariad/Incyte: Consultancy; Novartis: Consultancy; Gilead: Other: Travel; GSO: Other: Travel; Pfizer: Research Funding. Heuser:Karyopharm Therapeutics Inc: Research Funding; Pfizer: Research Funding; Bayer Pharma AG: Research Funding; Celgene: Honoraria; Tetralogic: Research Funding; BerGenBio: Research Funding; Novartis: Consultancy, Research Funding. Schlenk:Pfizer: Honoraria, Research Funding; Amgen: Research Funding.