Key Points North American ATLL has a distinct genomic landscape with a high frequency of prognostic epigenetic mutations, including EP300 mutations. ATLL samples with mutated EP300 have compromised p53 function and are selectively sensitive to decitabine treatment.

Introduction: TP53 mutant (mTP53) MDS and AML, accounting for 5-10% of de novo MDS and 25-30% of therapy related MDS (t-MDS), represent a distinct molecular cohort with inferior outcomes. Hypomethylating agents (HMA) are preferred treatments for patients (pts) with these mutations, although with CR rates of only 20-30% and median OS of 6-12 months. APR-246 is a novel, first-in-class small molecule that selectively induces apoptosis in mTP53 cancer cells through mutant p53 protein re-activation by restoring the wild-type conformation, with single agent activity in mTP53 AML. We report the planned, completed Phase 1b results of APR-246+ azacitidine (AZA) in mTP53 MDS/AML. Methods: This is a multicenter Phase 1b/2 trial of APR-246+AZA in HMA naïve mTP53 MDS and oligoblastic AML (≤ 30% blasts) pts ≥ 18 years of age. Pts received APR-246 in a 3+3 dose escalation design (50, 75, 100 mg/kg lean body weight (equivalent to 4500mg fixed dose based on PK studies)) IV daily over 4 days in a lead-in phase (days -14 to -10) followed by the same dose of APR-246 (days 1-4) + AZA 75 mg/m2 SC/IV over 7 days (days 4-10 or 4-5 and 8-12) in 28 day cycles. The primary objective was to define safety and the recommended Phase 2 dose (RP2D), with AEs graded by CTCAE v4.03 and DLT assessment over 6 weeks. Secondary objectives included response by IWG 2006 criteria as well as serial next generation sequencing (NGS) and p53 IHC for evaluation of clonal suppression and remission depth as predictors of outcomes. For minimal residual disease (MRD) analysis, a custom target-capture NGS assay was developed using unique molecular Identifiers for error correction with a limit of detection of 0.1% with results validated by pt specific digital droplet PCR (ddPCR). Nanostring nCounter RNA expression analysis was conducted on a panel of 770 genes after the lead-in phase to assess transcriptional effects induced by APR-246. Results: As of July 30, 2018, 12 pts (42% male; median age 66 years (39-73)) were enrolled. Three pts had AML-MRC and 9 had MDS; all pts had poor risk cytogenetics (17% poor, 83% very poor) and higher risk disease by IPSS-R (25% high, 75% very high). T-MDS occurred in 5 pts (42%) and 7 pts (58%) were transfusion-dependent at baseline. Median BM blasts were 9% (4-30). Eleven of 12 pts (92%) had a TP53 missense mutation in the DNA binding domain with multiple mutations in 4/12 pts (33%). For 9/12 pts (75%), TP53 was the sole mutation. Median time on study is 176 days (41-298) with 7 pts ongoing. Treatment (Tx) related AEs during the lead-in phase (all G1) included nausea (n=5), neuropathy (n=5), decreased appetite (n=2), and dizziness (n=2) which were all transient. Tx related AEs occurring in > 1 pt in the combination phase included nausea/vomiting (n=6), dizziness (n=3), headache (n=3), neuropathy (n=3), fall (n=2), pruritus (n=2), thrombocytopenia (n=6), neutropenia (n=5), and leukopenia (n=4); all G1/G2 except cytopenias (G3/G4). No DLTs have occurred to date. Eleven of twelve pts were response evaluable with 1 pt discontinuing tx prior to 1st disease assessment (Fig 1A). ORR by IWG was 100% (11/11) with 9 CR (82%) and 2 marrow CR (mCR; 18%). Median time to first response was 70 days (4-91) and one CR patient achieved mCR and partial cytogenetic response after APR-246 lead-in prior to combination therapy. All CR pts had high p53 positivity by IHC at baseline (25-80%) which normalized on serial assessment with the 2mCR pts having <5% p53+ at baseline. Serial NGS with a variant allele frequency (VAF) cutoff of 5% was negative in 73% of patients (8/11). In NGS negative pts, MRD analysis, validated by ddPCR, was performed with a median VAF of 0.3% (0.1%-3.1%) at best molecular response. Enriched pathway analysis via Reactome following APR-246 lead-in phase showed transcriptional activation of p53 targets (FDR = 9.16E-09), including pathways involved in cell cycle arrest, apoptosis, DNA repair, and regulation of TP53 activity. At a median follow up of 7 months, the median OS or PFS has not been reached. In comparison to a internal historical cohort of 51 mTP53 MDS/AML treated with AZA alone, APR-246+AZA had a trend for improved OS (NR vs 7.6months; HR 0.30, P=0.07; Fig 1B). Conclusions: APR-246+AZA combination is well tolerated in mTP53 MDS/AML. Responses have been achieved in all evaluable pts (82% CR) accompanied by deep molecular and durable remissions. The RP2D of APR-246 is a fixed dose of 4500mg days 1-4 in combination with AZA and phase 2 accrual has begun. Disclosures Sallman: Celgene: Research Funding, Speakers Bureau. Sweet:Agios: Consultancy; Phizer: Consultancy; Agios: Consultancy; BMS: Honoraria; Celgene: Honoraria, Speakers Bureau; Jazz: Speakers Bureau; Celgene: Honoraria, Speakers Bureau; BMS: Honoraria; Phizer: Consultancy; Novartis: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Astellas: Consultancy; Jazz: Speakers Bureau; Astellas: Consultancy. Cluzeau:Celgene: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; AbbVie: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pfizer: Speakers Bureau; Sanofi: Speakers Bureau; Menarini: Consultancy; Amgen: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Jazz Pharma: Consultancy, Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Sekeres:Opsona: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees; Opsona: Membership on an entity's Board of Directors or advisory committees; Celgene: Membership on an entity's Board of Directors or advisory committees. Roboz:Orsenix: Consultancy; Cellectis: Research Funding; Eisai: Consultancy; Astex Pharmaceuticals: Consultancy; Argenx: Consultancy; Pfizer: Consultancy; Bayer: Consultancy; Eisai: Consultancy; Sandoz: Consultancy; Jazz Pharmaceuticals: Consultancy; Jazz Pharmaceuticals: Consultancy; Novartis: Consultancy; Pfizer: Consultancy; Otsuka: Consultancy; Bayer: Consultancy; Aphivena Therapeutics: Consultancy; Celltrion: Consultancy; Argenx: Consultancy; Celgene Corporation: Consultancy; Daiichi Sankyo: Consultancy; Celltrion: Consultancy; Sandoz: Consultancy; Astex Pharmaceuticals: Consultancy; Aphivena Therapeutics: Consultancy; Orsenix: Consultancy; Otsuka: Consultancy; Roche/Genentech: Consultancy; Roche/Genentech: Consultancy; Janssen Pharmaceuticals: Consultancy; Daiichi Sankyo: Consultancy; Novartis: Consultancy; AbbVie: Consultancy; Janssen Pharmaceuticals: Consultancy; Celgene Corporation: Consultancy; AbbVie: Consultancy; Cellectis: Research Funding. Bhagat:Genoptix: Employment. Tell:Aprea Therapeutics: Employment. Fenaux:Celgene: Honoraria, Research Funding; Janssen: Honoraria, Research Funding; Jazz: Honoraria, Research Funding; Otsuka: Honoraria, Research Funding; Roche: Honoraria. List:Celgene: Research Funding. Komrokji:Novartis: Honoraria, Speakers Bureau; Celgene: Honoraria, Research Funding; Novartis: Honoraria, Speakers Bureau; Celgene: Honoraria, Research Funding; Novartis: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau.

Key Points Leukemia-associated mutations can be detected many years before the onset of secondary leukemias in myeloma patients. Stem and progenitor cells can act as reservoirs of mutations before the onset of secondary MDS and AML after treatment of myeloma.

Introduction The identification of somatic genomic alterations in cancer has brought forth a paradigm change in the personalized management of patients with acute myeloid leukemia (AML). This is exemplified by the recent FDA approvals with the targeted small molecule inhibitors of mutant IDH1 (ivosidenib) and IDH2 (enasidenib) for patients with relapsed/refractory AML. IDH1/2 mutations have been reported to occur in approximately 16-20% of patients with AML based on the largest published cohorts to date (Dinardo et al., Am J Hematol, 2015; Papaemmanuil et al., NEJM, 2016). However, there remains a paucity of data on the frequency of IDH1/2 and other targetable mutations in extramedullary manifestations of AML (i.e. myeloid sarcoma and leukemia cutis; EM-AML). We sought to characterize the mutational landscape of EM-AML, with a focus on determining the frequency of IDH1/2 mutations. Methods This is a multi-institutional retrospective analysis of patients diagnosed with EM-AML, who were treated at Moffitt Cancer Center or Memorial Healthcare System and underwent next-generation sequencing (NGS). All patients were evaluated for IDH1/2 mutations and up to 435 additional genes. Clinical variables and outcomes of EM-AML patients were characterized at the time of sample procurement. Additionally, we acquired additional de-identified NGS data on EM-AML patients who underwent sequencing of the EM site at Genoptix. We describe the mutational landscape of patients and compared the frequency of IDH1/2 mutations to historical controls in AML from the published literature using Fisher's exact test. Kaplan-Meier curves were used to estimate overall survival (OS) and analyzed from the date of mutation identification. Results Thirty-five patients with EM-AML were identified (22 in the clinical cohort and 13 in the Genoptix cohort) and are included in this analysis. The distribution of EM-AML diagnoses were myeloid sarcoma in 71% of cases (n=25) and leukemia cutis in 29% (n=10). The sequenced samples were from an extramedullary site for 63% (n=22) of the cases. The median age of the cohort was 64 (IQR 52 - 72) with a male predominance (55%). Of the clinical cohort, 68% (n=15) were non-Hispanic White, 23% (n=5) were Hispanic, and 9% (n=2) were Black. The molecular landscape of the cohort is shown in Figure 1. The frequency of IDH1/2 mutations was 31% (11/35), with IDH1 and IDH2 mutations reported in 17% (n=6) and 14% (n=5) of cases, respectively. All IDH1 mutations were at position R132 (4 R132H and 2 R132C) and all IDH2 mutations were at R140 (4 R140Q and 1 R140G). The other most frequent genomic alterations were DNMT3A (29%), NPM1 (26%), FLT3 (23%; ITD in 18% and TKD in 5%; 11% in IDH wildtype), NRAS (21%), TET2 (17%), and ASXL1 (17%). Mutations in DNA methylation occurred in 54% of patients (n=19). Co-occurring NRAS/KRAS mutations were more frequent in IDH mutant patients (45%; 5/11) compared to 12% (3/24) of IDH wild type patients (P=0.01). DNMT3A mutations were reported in 45% (5/11) of IDH mutant cases compared to 21% (5/24) of IDH wildtype cases, although this was not statistically significant (P=0.23). In comparison to a historical frequency of IDH1/2 mutations in AML patients of 17.4% (n=2366), EM-AML patients had an increased frequency of 31% (P=0.04). The median OS of the cohort was 13.6 months. Within the clinical cohort 50% (4/8) of the IDH1/2 mutant patients were treated with an IDH inhibitor with CR in 1 patient, CRi in 1 patient, and stable disease in 2 patients. The patient who achieved CR developed widespread leukemia cutis during cycle 1 of enasidenib which resolved over 6 months and is in durable CR for 15 months. Conclusion Overall, EM-AML patients had targetable mutations (i.e. IDH1/IDH2/FLT3) in 40% of cases with an increased frequency of IDH1/2 mutations (31%) in comparison to the general AML population. IDH mutant EM-AML patients achieved clinical benefit to specific inhibitors. These data support mutational analysis of EM-AML patients in order to personalize therapeutic options for our patients. Figure 1. Figure 1. Disclosures Bhagat: Genoptix: Employment. Watts:Takeda: Research Funding; Jazz Pharma: Consultancy, Speakers Bureau. Sweet:Novartis: Consultancy, Honoraria, Speakers Bureau; Novartis: Consultancy, Honoraria, Speakers Bureau; Jazz: Speakers Bureau; Celgene: Honoraria, Speakers Bureau; Jazz: Speakers Bureau; BMS: Honoraria; Astellas: Consultancy; Celgene: Honoraria, Speakers Bureau; Astellas: Consultancy; Agios: Consultancy; Agios: Consultancy; Phizer: Consultancy; Phizer: Consultancy; BMS: Honoraria. Komrokji:Celgene: Honoraria, Research Funding; Novartis: Honoraria, Speakers Bureau; Celgene: Honoraria, Research Funding; Novartis: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Novartis: Honoraria, Speakers Bureau. Sallman:Celgene: Research Funding, Speakers Bureau.

Introduction: TP53 mutant (mTP53) MDS and AML represent a distinct molecular cohort with poor outcomes. Hypomethylating agents (HMA) have emerged as preferred treatment for these patients with CR rate of 20-30% and median OS of 6-12 months. APR-246 is a mutant p53 activator with single agent activity in mTP53 AML. We report initial phase 1b results of APR-246 + AZA in mTP53 MDS/AML. Methods: Eligible pts included HMA naïve mTP53 MDS and oligoblastic AML (≤ 30% blasts) ≥ 18 years of age. Pts received APR-246 in a 3+3 dose escalation design (50, 75, 100 mg/kg lean body weight) IV daily over 4 days in a lead-in phase (days -14 to -10) followed by the same dose of APR-246 (days 1-4) + AZA 75 mg/m2 SC/IV over 7 days (days 4-10 or 4-5 and 8-12) in 28 day cycles. Primary objective was safety with AEs graded by CTCAE v4.03 and DLT assessment over 6 weeks. Secondary endpoints included response by IWG 2006 criteria as well as serial next generation sequencing (NGS) and p53 IHC for evaluation of clonal suppression and remission depth. Results: As of Jan 1, 2017, 9 pts (33% male; median age 65 years (39-73)) have enrolled with 3 pts per cohort. Three pts had AML-MRC and 6 had MDS; all pts had poor risk cytogenetics (11% poor, 89% very poor) and higher risk disease by IPSS-R (22% high, 78% very high). Median BM blasts were 18% (4-30). Seven pts (78%) remain on study: 2 pts in the 50mg/kg cohort discontinued treatment (Tx), 1 pt due to infection during C2 who later died of sepsis unrelated to Tx, and 1 pt electively discontinued in durable marrow CR (mCR) after 5 cycles of therapy. Median time on study is 106 days (14-221). Tx related AEs during the lead-in phase (all G1) included ataxia (n=1), dizziness (n=1), and facial numbness (n=1). AEs occurring in &gt; 1 pt included dizziness (n=3), nausea (n=3), neutropenia (n=3), thrombocytopenia (n=3), infection (n=3), headache (n=2), pain (n=2), weakness (n=2), falls (n=2), facial numbness (n=2), and ataxia (n=2); all G1/G2 except neutropenia/thrombocytopenia (G4). No Tx-related SAEs or DLTs have occurred to date. Five of six pts were response evaluable with 1 pt discontinuing tx prior to 1st disease assessment. ORR by IWG was 100% with 4 CR (80%, 3/3 in DL2) and 1 mCR. All CR patients achieved complete cytogenetic response. One CR patient achieved a mCR and partial cytogenetic response after APR-246 lead-in prior to combination therapy. All CR pts had high p53 positivity by IHC at baseline (55-70%) which normalized on serial assessment (&lt;5%). Serial NGS with a variant allele frequency (VAF) cutoff of 2% was negative in 80% of patients (4/5). The remaining 3 pts entered the study in Dec 17/Jan 18 with no response data available at data cutoff. Conclusions: APR-246 + AZA combination is well tolerated in mTP53 MDS/AML. Responses have been achieved in all pts (80% CR) accompanied by deep molecular remissions. The maximum tolerated dose has not been reached and dose escalation is ongoing. Citation Format: David A. Sallman, Amy DeZern, Kendra Sweet, David P. Steensma, Thomas Cluzeau, Mikkael Sekeres, Guillermo Garcia-Manero, Gail Roboz, Amy McLemore, Kathy McGraw, John Puskas, Ling Zhang, Chirag Bhagat, Armin Graber, Najla H. Al Ali, Eric Padron, Roger Tell, Jeffrey E. Lancet, Pierre Fenaux, Alan F. List, Rami S. Komrokji. Phase Ib/II combination study of APR-246 and azacitidine (AZA) in patients with TP53 mutant myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr CT068.