Abstract: Biallelic mutations of the CEBPA gene (CEBPAbi) define a distinct entity associated with favorable prognosis; however, the role of monoallelic mutations (CEBPAsm) is poorly understood. We retrospectively analyzed 4708 adults with acute myeloid leukemia (AML) who had been recruited into the Study Alliance Leukemia trials, to investigate the prognostic impact of CEBPAsm. CEBPA mutations were identified in 240 patients (5.1%): 131 CEBPAbi and 109 CEBPAsm (60 affecting the N-terminal transactivation domains [CEBPAsmTAD] and 49 the C-terminal DNA-binding or basic leucine zipper region [CEBPAsmbZIP] ). Interestingly, patients carrying CEBPAbi or CEBPAsmbZIP shared several clinical factors: they were significantly younger (median, 46 and 50 years, respectively) and had higher white blood cell (WBC) counts at diagnosis (median, 23.7 × 109/L and 35.7 × 109/L) than patients with CEBPAsmTAD (median age, 63 years, median WBC 13.1 × 109/L; P & lt; .001). Co-mutations were similar in both groups: GATA2 mutations (35.1% CEBPAbi; 36.7% CEBPAsmbZIP vs 6.7% CEBPAsmTAD; P & lt; .001) or NPM1 mutations (3.1% CEBPAbi; 8.2% CEBPAsmbZIP vs 38.3% CEBPAsmTAD; P & lt; .001). CEBPAbi and CEBPAsmbZIP, but not CEBPAsmTAD were associated with significantly improved overall (OS; median 103 and 63 vs 13 months) and event-free survival (EFS; median, 20.7 and 17.1 months vs 5.7 months), in univariate and multivariable analyses. Additional analyses revealed that the clinical and molecular features as well as the favorable survival were confined to patients with in-frame mutations in bZIP (CEBPAbZIP-inf). When patients were classified according to CEBPAbZIP-inf and CEBPAother (including CEBPAsmTAD and non-CEBPAbZIP-inf), only patients bearing CEBPAbZIP-inf showed superior complete remission rates and the longest median OS and EFS, arguing for a previously undefined prognostic role of this type of mutation.

Abstract: Abstract 2060 Poster Board II-37 Introduction: The Flt3-internal tandem duplication can be found in up to 30% of all acute myeloid leukemia (AML) patients and confers a poor risk status characterized by an increased relapse rate and poor overall survival. Moreover, Flt3-ITD-positive AML patients relapsing after allogenic stem cell transplantation (SCT) have very limited therapeutic options. Sorafenib is a multikinase inhibitor that is approved for the treatment of metastatic renal cell and hepatocellular carcinoma. Besides targeting Raf, the platelet derived growth factor receptor (PDGFR) and the vascular endothelial growth factor receptor (VEGFR) it has also significant inhibitory activity against the Flt3 receptor tyrosine kinase, and, specifically the mutated variant of Flt3, Flt3-ITD. It has previously been shown that sorafenib monotherapy may have considerable activity in relapsed Flt3-ITD positive AML. Nevertheless, clinical experience is still limited. Here we report compassionate use experience on 18 relapsed or refractory Flt3-ITD positive AML patients treated with sorafenib monotherapy. Methods: A questionnaire was developed and sent to 28 centers in Germany in order to obtain more insight into the clinical efficacy and tolerablilty of sorafenib monotherapy in Flt3-ITD positive AML. Forms were returned from 13 centers, reporting 26 patients. Among them, eight had to be excluded from further analysis. Five of them were Flt3-ITD mutation negative and three received contemporary chemotherapy. Available patient information included age, FAB-classification, karyotype, type and response to prior therapy, sorafenib dosing, tolerability, treatment duration, and response. Results: Of the 18 patients (12 male, 6 female), five were primary refractory to induction chemotherapy and 13 received sorafenib in first (n=11) or second (n=2) relapse. Eight of 18 patients relapsed after SCT and were treated with sorafenib. One patient was treated for steadily increasing Flt3-ITD copy numbers, that is, in molecular relapse after SCT. Patients received between 200mg and 800mg sorafenib p.o. daily. The median treatment duration was 98 days (range, 16-425 days). All patients achieved a hematological response (HR) characterized by complete (n=17) or near complete peripheral blast clearance (n=2). Of the 18 patients the documented best response to sorafenib were: HR in 9 cases, bone marrow response (HR and blast reduction in marrow) in 4 cases, complete remission (normalization of peripheral blood counts and bone marrow blasts 〈 5%) in one case and complete molecular remission (molecular negativity for Flt3-ITD) in 4 patients. After a median treatment duration of 180 days (range, 82-270 days) 7 of the 18 (39%) patients developed clinical sorafenib resistance: two of eight (25%) of the SCT-group and 5 of 10 (50%) of the non-SCT group. Sorafenib was generally well tolerated. Pancytopenia or thrombocytopenia grade III and IV were the most significant side effects, observed in 13 patients. Other reported side effects such as diarrhea, exanthema were documented from the centers as being minor. Conclusion: Sorafenib monotherapy has significant clinical activity in Flt3-ITD positive relapsed and refractory AML and may be particularly effective in the context of allo-immunotherapy where 3 CMR could be seen. Disclosures: Enghofer: Bayer Schering Pharma: Employment. Off Label Use: sorafenib, used to treat Flt3-ITD positive AML patients.

Abstract: Abstract 3314 Introduction: The FLT3-internal tandem duplication is the most frequent genetic aberration in normal karyotype acute myeloid leukemia (NK-AML) and associated with a poor prognosis. Patients with FLT3-ITD positive AML relapsing after allogenic stem cell transplantation (allo-SCT) have very limited therapeutic options. Sorafenib is a multikinase inhibitor, which is approved in Europe for the treatment of metastatic renal cell and hepatocellular carcinoma. It inhibits the FLT3 receptor tyrosine kinase, and, at low nanomolar concentrations also the mutated variant of FLT3, FLT3-ITD. Sorafenib also inhibits Raf, the platelet derived growth factor receptor (PDGFR) and the vascular endothelial growth factor receptor (VEGFR). We have previously reported that sorafenib monotherapy is effective in relapsed FLT3-ITD positive AML (Metzelder et al., Blood 2009; Metzelder et al., ASH 2009, poster #2060). Here we significantly extend these compassionate use experiences by reporting on clinical response details from 39 relapsed or refractory FLT3-ITD positive AML patients treated with sorafenib monotherapy. Methods: A questionnaire was developed and sent to 60 centers in Germany, Singapore and the United States, where FLT3-ITD-positive patients had been treated with sorafenib monotherapy. 26 centers returned information on therapy details of 55 patients. These included data on age, FAB-classification, karyotype, FLT3-ITD molecular testing, type and duration of response to prior therapy and to sorafenib, sorafenib dosing and tolerability. 16 patients were excluded from further analysis because of FLT3-ITD negativity or application of chemotherapy concomitant to sorafenib. Results: There were 39 evaluable patients (20 male, 19 female), grouped into i) primary refractory patients (PR-P) (n=11), receiving one (n=5) or two cycles (n=6) of chemotherapy before commencing sorafenib, ii) relapsing patients (REL-P) (n=12) with hematological recurrence after between one and four cycles of prior chemotherapy, syngenic, or autologous SCT, and iii) patients relapsing after allogenic SCT (SCT-P) (n=16). One patient was treated first line with sorafenib. One patient was treated before and after allo-SCT. Patients received between 200mg and 800mg sorafenib p.o. daily. The median treatment duration was 71 days (range, 13 to 270) for PR-P, 76 days (range, 9 to 160 days) for REL-P, and 76 days (range, 20 to 489 days) for SCT-P. All reported patients in this cohort responded to sorafenib. In the PR-P group, there were 6 hematological remissions (HR), characterized by complete (n=4) or near complete peripheral blast clearance (n=2), 4 complete remissions (bone marrow blasts 〈 5% with (CR) or without (CRp) normalization of peripheral blood counts) and one complete molecular remission (CMR, molecular negativity for FLT3-ITD). Six of these 11 PR-P underwent allo-SCT after responding to sorafenib induction. In the REL-P group there was one patient with a partial blast clearance (PR), 8 HR, 2 bone marrow responses (which includes a HR) and 1 CRp. In the SCT-P group there were 3PR, 2HR, 7 BMR and 4 CMR. Notably, the median time to treatment failure due to frank clinical sorafenib resistance was 119 days for PR-P and REL-P, but was not reached in the SCT-P group. This difference was statistically significant (p-value 0.0217). Sorafenib was generally well tolerated. Pancytopenia or thrombocytopenia grade III and IV were the most significant but manageable side effects. Other reported side effects such as diarrhea, exanthema were documented from the centers as being minor. Conclusion: This analysis on a large cohort of 39 FLT3-ITD positive patients confirms our previous reports on the remarkable clinical activity of sorafenib monotherapy in FLT3-ITD positive AML. Evidence is accumulating that sorafenib may be particularly effective in the context of allo-SCT, where long-term responses were seen. Disclosures: No relevant conflicts of interest to declare.

Abstract: Functional perturbations of the cohesin complex with subsequent changes in chromatin structure and replication are reported in a multitude of cancers including acute myeloid leukemia (AML). Mutations of its STAG2 subunit may predict unfavorable risk as recognized by the 2022 European Leukemia Net recommendations, but the underlying evidence is limited by small sample sizes and conflicting observations regarding clinical outcomes, as well as scarce information on other cohesion complex subunits. We retrospectively analyzed data from a multi-center cohort of 1615 intensively treated AML patients and identified distinct co-mutational patters for mutations of STAG2 , which were associated with normal karyotypes (NK) and concomitant mutations in IDH2 , RUNX1, BCOR, ASXL1 , and SRSF2 . Mutated RAD21 was associated with NK, mutated EZH2, KRAS, CBL , and NPM1 . Patients harboring mutated STAG2 were older and presented with decreased white blood cell, bone marrow and peripheral blood blast counts. Overall, neither mutated STAG2, RAD21, SMC1A nor SMC3 displayed any significant, independent effect on clinical outcomes defined as complete remission, event-free, relapse-free or overall survival. However, we found almost complete mutual exclusivity of genetic alterations of individual cohesin subunits. This mutual exclusivity may be the basis for therapeutic strategies via synthetic lethality in cohesin mutated AML.

Abstract: Tandem-duplication mutations of the UBTF gene ( UBTF -TDs) coding for the upstream binding transcription factor have recently been described in pediatric patients with acute myeloid leukemia (AML) and were found to be associated with particular genetics (trisomy 8 (+8), FLT3 -internal tandem duplications ( FLT3 -ITD), WT1 -mutations) and inferior outcome. Due to limited knowledge on UBTF- TDs in adult AML, we screened 4247 newly diagnosed adult AML and higher-risk myelodysplastic syndrome (MDS) patients using high-resolution fragment analysis. UBTF -TDs were overall rare ( n  = 52/4247; 1.2%), but significantly enriched in younger patients (median age 41 years) and associated with MDS-related morphology as well as significantly lower hemoglobin and platelet levels. Patients with UBTF -TDs had significantly higher rates of +8 (34% vs. 9%), WT1 (52% vs. 7%) and FLT3 -ITD (50% vs. 20.8%) co-mutations, whereas UBTF -TDs were mutually exclusive with several class-defining lesions such as mutant NPM1 , in-frame CEBPA bZIP mutations as well as t(8;21). Based on the high-variant allele frequency found and the fact that all relapsed patients analyzed ( n  = 5) retained the UBTF -TD mutation, UBTF -TDs represent early clonal events and are stable over the disease course. In univariate analysis, UBTF -TDs did not represent a significant factor for overall or relapse-free survival in the entire cohort. However, in patients under 50 years of age, who represent the majority of UBTF -mutant patients, UBTF -TDs were an independent prognostic factor for inferior event-free (EFS), relapse-free (RFS) and overall survival (OS), which was confirmed by multivariable analyses including established risk factors such as age and ELN2022 genetic risk groups (EFS [HR: 2.20; 95% CI 1.52–3.17, p   〈  0.001], RFS [HR: 1.59; 95% CI 1.02–2.46, p  = 0.039] and OS [HR: 1.64; 95% CI 1.08–2.49, p  = 0.020]). In summary, UBTF -TDs appear to represent a novel class-defining lesion not only in pediatric AML but also younger adults and are associated with myelodysplasia and inferior outcome in these patients.

Abstract: Purpose Mutations of the isocitrate dehydrogenase-1 (IDH1) and IDH2 genes are one of the most frequent alterations in acute myeloid leukemia (AML) and can be found in ~20% of patients at diagnosis. Several IDH inhibitors are currently in late stage clinical development with Enasidenib, an IDH2 inhibitor, being recently approved by the FDA. Previous analyses have reported differential impact on response to chemotherapy and outcome, depending on the IDH-mutation type, co-occurring mutations and cytogenetic abnormalities, as well as the variant allele frequency (VAF) of IDH mutations. In order to better understand its prognostic role, we analyzed newly diagnosed AML patients enrolled in prospective trials of the Study Alliance Leukemia (SAL) to investigate the impact of IDH1/2 mutations on outcome. Patients and Methods All AML patients consecutively enrolled into intensive AML treatment protocols of the SAL or into the SAL registry were included in this analysis. Next-generation sequencing (NGS) on an Illumina MiSeq-system was performed to detect IDH1/2 mutations using pre-treatment samples. Overall survival (OS) and response to therapy were analyzed for all patients with intensive treatment and according to the mutational status. Results Overall, samples of 3898 patients were analyzed. The median follow-up was 91 months (95% CI 87.2 - 93.9). Patients' characteristics are shown in Tbl.1. Three-hundred twenty-nine patients (8.4%) had IDH1 mutations and 423 (11%) had IDH2 mutations; both mutations were found in 12 pts, so the overall mutation rate in IDH1 and 2 was 19% (740/3898 patients). Of the IDH1 variants, the most common ones were the R132C found in 143 patients (43%) and R132H in 137 patients (42%). For IDH2, 324 patients had the R140Q (77%) and 80 patients the R172K (19%) variant. According to the two main variants of the more common IDH2 mutations, as reported before, the IDH2 R172K was mutually exclusive with NPM1 and/or FLT3-ITD mutations. Overall, there was a trend for increased OS for patients with IDH2 R172K (26 vs. 15 months) as compared to those with R140Q. Considering only patients with a normal karyotype and no NPM1/FLT3-ITD mutation, these patients (n=27) had a highly significant better OS than patients with IDH2 R140Q (46.3 vs. 13.1 months, p=.012), supporting the findings published by Papaemmanuil et al. (NEJM 2016). In IDH1-mutated patients, we observed statistically significant differences in baseline characteristics between the two most common mutation types, IDH1 R132C and R132H. Patients carrying the R132C mutation were older (62 vs. 55 years, p=.001), had lower WBC (3.6 vs. 21 Gpt/L, p≤.001) and were less likely to have a normal karyotype (43% vs. 66%, p=.002), NPM1 (23% vs. 66%, p= 〈 .001), and FLT3-ITD mutations (8% vs. 27%, p 〈 .001) than those with the R132H variant. In univariate testing, the CR rate was also statistically significant lower in patients with IDH1 R132C (53% vs. 72%, p≤.001), with a median OS of 12.9 months compared to 17.4 months for patients with R132H variant (p=.08). In multivariate analysis including age, WBC, NPM1 and FLT3 status, and ELN risk, the CR rate was significantly lower in patients with the IDH1 R132C variant (p=.038). The median IDH VAF was 38% (range, 0.1 - 58) with no difference according to the different types of mutation. Patients with a VAF 〉 30% had a significantly higher BM blast count (73% vs 40% for VAF≤5%) and WBC (21.2 Gpt/L vs. 3.7 Gpt/L) at baseline, but there was no clear impact on CR rate or OS found in multivariate analysis. Conclusion In this large cohort of AML patients with IDH1/2 mutations, we found significant and so far not reported differences for one of the two most prominent mutations types of IDH1. The R132C variant was associated with increased age, lower WBC, and lower NPM1 and/or FLT3 co-mutation rate. Further, these patients had lower CR rates and a trend for shorter OS. For IDH2 we were able to reproduce findings on co-mutations and showed a favorable outcome for intensively treated patients with a normal karyotype and no NPM1/FLT3-ITD mutation and the IDH2 R172K variant, providing additional evidence for classification as a separate AML entity. Disclosures Middeke: Roche: Membership on an entity's Board of Directors or advisory committees; Janssen: Membership on an entity's Board of Directors or advisory committees, Research Funding; Abbvie: Membership on an entity's Board of Directors or advisory committees. Rollig:Bayer: Research Funding; Janssen: Research Funding. Kramer:Roche: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Bayer: Research Funding; Daiichi Sankyo: Consultancy. Scholl:Alexion: Other: Travel support; Abbivie: Other: Travel support; Novartis: Other: Travel support; Deutsche Krebshilfe: Research Funding; Carreras Foundation: Research Funding; Pfizer: Membership on an entity's Board of Directors or advisory committees; MDS: Other: Travel support; Jazz Pharma: Membership on an entity's Board of Directors or advisory committees. Hochhaus:Incyte: Research Funding; Pfizer: Research Funding; Takeda: Research Funding; Bristol-Myers Squibb: Research Funding; Novartis: Research Funding. Brümmendorf:Takeda: Consultancy; Pfizer: Consultancy, Research Funding; Janssen: Consultancy; Merck: Consultancy; Novartis: Consultancy, Research Funding. Burchert:Novartis: Research Funding; Pfizer: Honoraria; Bristol Myers Squibb: Honoraria, Research Funding; AOP Orphan: Honoraria, Research Funding; Bayer: Research Funding. Krause:Novartis: Research Funding. Hänel:Amgen: Honoraria; Novartis: Honoraria; Roche: Honoraria; Takeda: Honoraria. Platzbecker:Celgene: Research Funding. Mayer:Johnson & Johnson: Research Funding; Roche: Research Funding; Eisai: Research Funding; Affimed: Research Funding; Novartis: Research Funding. Serve:Bayer: Research Funding. Ehninger:Cellex Gesellschaft fuer Zellgewinnung mbH: Employment, Equity Ownership; Bayer: Research Funding; GEMoaB Monoclonals GmbH: Employment, Equity Ownership. Schetelig:Gilead: Consultancy, Honoraria, Research Funding; Abbvie: Honoraria; Janssen: Consultancy, Honoraria; Roche: Honoraria; Sanofi: Consultancy, Research Funding; Novartis: Consultancy, Honoraria, Research Funding. Thiede:AgenDix: Other: Ownership; Novartis: Honoraria, Research Funding. Stoelzel:Neovii: Speakers Bureau.

Abstract: Acute myeloid leukemia (AML) is characterized by recurrent genetic events. The BCL6 corepressor (BCOR) and its homolog, the BCL6 corepressor-like 1 (BCORL1), have been reported to be rare but recurrent mutations in AML. Previously, smaller studies have reported conflicting results regarding impacts on outcomes. Here, we retrospectively analyzed a large cohort of 1529 patients with newly diagnosed and intensively treated AML. BCOR and BCORL1 mutations were found in 71 (4.6%) and 53 patients (3.5%), respectively. Frequently co-mutated genes were DNTM3A, TET2 and RUNX1. Mutated BCORL1 and loss-of-function mutations of BCOR were significantly more common in the ELN2017 intermediate-risk group. Patients harboring loss-of-function mutations of BCOR had a significantly reduced median event-free survival (HR = 1.464 (95%-Confidence Interval (CI): 1.005–2.134), p = 0.047), relapse-free survival (HR = 1.904 (95%-CI: 1.163–3.117), p = 0.01), and trend for reduced overall survival (HR = 1.495 (95%-CI: 0.990–2.258), p = 0.056) in multivariable analysis. Our study establishes a novel role for loss-of-function mutations of BCOR regarding risk stratification in AML, which may influence treatment allocation.