Kapsalis, Stephanie M.

Introduction Patients (pts) with relapsed/refractory (R/R) myelodysplastic syndromes (MDS) have a poor prognosis and, until recently, lacked therapeutic options. Ivosidenib (IVO) is an oral, targeted, small-molecule inhibitor of mIDH1. In October 2023, IVO was granted FDA approval for the treatment of adult pts with mIDH1 R/R MDS on the basis of results from the pivotal AG120-C-001 MDS substudy (NCT02074839); IVO showed an acceptable safety profile and induced durable remissions, with a high rate (38.9%) of complete remissions (CR) per International Working Group (IWG) 2006 criteria (DiNardo et al. Blood Adv 2024; bloodadvances.2023012302.). Response criteria evolve to better reflect clinical benefit in specific pt populations and reduce interobserver variability. The updated IWG 2023 criteria for higher-risk MDS lowered the hemoglobin threshold for CR, added response categories for pts with <5% blasts or limited count recovery, and eliminated the marrow CR (mCR) category. Herein we analyze responses, transfusion independence (TI), and survival outcomes of pts treated with IVO according to IWG 2023 criteria. In addition, responses assessed per IWG 2023 and IWG 2006 criteria are compared. Methods Pts with mIDH1 R/R MDS who had received prior SOC therapy were eligible. Oral IVO 500 mg was administered daily on days 1-28 of 28-day cycles. Responses were assessed per IWG 2023 criteria, and a composite CR (CRc) category was included in the analysis, which comprises all CR categories: CR + CR equivalent (CRe) + CR with limited count recovery (CRL) + CR with partial hematologic recovery (CRh). Overall response rate (ORR) was defined as CR + mCR + partial remission (PR) per IWG 2006 criteria, and as CRc + PR + hematologic improvement (HI) per IWG 2023 criteria. For TI analysis, non-CRc was defined as HI + PR + no response (NR)/not evaluable + progressive disease. TI was defined as requiring no transfusion for ≥56 days. Results In total, 19 pts were enrolled (median age: 73 yr; prior hypomethylating therapy: 78.9%) and data from 18 efficacy-evaluable pts were analyzed. CR + PR rate (primary endpoint) per IWG 2006 was 38.9%, with all 7 (38.9%) responders having CR. CRc + PR rate per IWG 2023 was 66.7% (n=12), with all responders having CRc, including 5 (27.8%) pts with CR, 3 (16.7%) with CRe, and 4 (22.2%) with CRL (CR unilineage [CRLuni], n=2 [11.1%]; CR bilineage [CRLbi], n=2 [11.1%]); no pt had CRh or PR. ORR was 83.3% per IWG 2006, with 7 (38.9%) pts having CR and 8 (44.4%) mCR; 4 (22.2%) pts with mCR had HI. Per IWG 2023 criteria, the ORR was 72.2%, with 12 (66.7%) pts having CRc and 1 (5.6%) HI with neutrophil response. The 8 mCR per IWG 2006 criteria were reclassified as 1 CR, 4 CRL (2 CRLuni and 2 CRLbi), 1 HI, and 2 NR per IWG 2023. Median time to CRc was 1.58 mo. Median duration of CRc was not reached and Kaplan-Meier (KM) estimates at 3, 6, and 12 mo were 90.9%, 81.8%, and 68.2%, respectively. Five (CRc group n=4; non-CRc group n=1) of 7 (71.4%) and 3 (CRc, n=1; non-CRc, n=2) of 4 pts requiring red blood cell (RBC) and platelet transfusion at baseline, respectively, had TI. Median time to any (RBC/platelet) TI was 2.64 and 2.43 mo for pts with CRc and non-CRc, respectively. Moreover, 10 of 12 (83.3%) pts with CRc and 3 of 6 (50%) with non-CRc had or maintained TI during the study. Median duration of TI was not reached and KM estimates at 3 and 6 mo were 90.0% and 65.6%, respectively, for pts with CRc and 100% and 66.7% for non-CRc. Median event-free survival (EFS) was not reached for pts with CRc (n=12) or NR (n=5), and KM estimates at 1 yr were 68.2% and 53.3%, respectively. Median overall survival (OS) was not reached for pts with CRc and was 16.5 mo for pts with NR. For pts with CRc, OS KM estimates at 1, 3, and 5 yr were 90.9%, 51.1%, and 51.1%, respectively. For pts with NR, OS KM estimates were 75% at 1 yr and not estimable at 3 and 5 yr. For the pt with HI, the EFS estimate at 1 yr was 100% and OS estimates were 100% at 1, 3, and 5 yr. Conclusions IVO resulted in a high ORR (72.2%) according to IWG 2023 criteria, including a 66.7% CRc rate, despite the removal of the mCR category. Of 8 mCR per IWG 2006 criteria, 5 (62.5%) were reclassified as CRc per IWG 2023 criteria. By eliminating mCR and assessing response in a high-risk population with <5% blasts, IWG 2023 criteria accurately capture the clinical benefit of IVO in R/R MDS. While comparison of survival outcomes between IWG 2006 and IWG 2023 is limited by the small sample size, a similar trend with response-dependent EFS and OS outcomes was observed.

Abstract Ivosidenib is a first-in-class mutant isocitrate dehydrogenase 1 (mIDH1) inhibitor with efficacy and tolerability in patients with advanced mIDH1 hematologic malignancies, leading to approval in frontline and relapsed/refractory (R/R) mIDH1 acute myeloid leukemia. We report final data from a phase 1 single-arm substudy of once-daily ivosidenib in patients with R/R mIDH1 myelodysplastic syndrome (MDS) after failure of standard-of-care therapies. Primary objectives were to determine safety, tolerability, and clinical activity. The primary efficacy end point was the complete remission (CR) + partial remission (PR) rate. Nineteen patients were enrolled; 18 were included in the efficacy analysis. Treatment-related adverse events occurred in 8 (42.1%) patients, including a grade 1 QT interval prolongation in 1 (5.3%) patient and grade 2 differentiation syndrome in 2 (10.5%) patients. Rates of CR + PR and objective response (CR + PR + marrow CR) were 38.9% (95% confidence interval [CI], 17.3-64.3) and 83.3% (95% CI, 58.6-96.4), respectively. Kaplan-Meier estimates showed a 68.6% probability of patients in CR achieving a remission duration of ≥5 years, and a median overall survival of 35.7 months. Of note, 71.4% and 75.0% baseline red blood cell (RBC)- and platelet-transfusion-dependent patients, respectively, became transfusion independent (TI; no transfusion for ≥56 days); 81.8% and 100% of baseline RBC and platelet TI patients, respectively, remained TI. One (5.3%) patient proceeded to a hematopoietic stem cell transplant. In conclusion, ivosidenib is clinically active, with durable remissions and a manageable safety profile observed in these patients. This trial was registered at www.ClinicalTrials.gov as #NCT02074839.

7053 Background: Mutations in isocitrate dehydrogenase 1 ( IDH1) occur in ̃3% of patients (pts) with MDS and are associated with increased transformation to acute myeloid leukemia (AML). Ivosidenib (IVO), an oral, potent, targeted inhibitor of the mutant IDH1 (mIDH1) enzyme, is FDA approved for m IDH1 R/R AML and m IDH1 newly diagnosed AML in pts ≥75 years old or with comorbidities precluding the use of intensive induction chemotherapy. In the first-in-human study of IVO in pts with m IDH1 advanced hematologic malignancies (NCT02074839), 12 pts with R/R MDS received IVO 500 mg once daily (QD). Based on encouraging safety and efficacy findings, including an investigator-assessed overall response rate (ORR) of 75%, with median response duration of 21.4 months, the FDA granted Breakthrough Therapy designation to IVO in m IDH1 R/R MDS and the study was amended to enroll additional pts. We report updated results. Methods: This substudy of the single-arm, open-label study of IVO evaluated pts with R/R MDS after documented failure or relapse following prior standard therapy including intensive chemotherapy and hypomethylating agents. Other key eligibility criteria included: high disease burden based on IPSS or IPSS-R risk at baseline; an Eastern Cooperative Oncology Group performance status score of 0–2; and no prior IDH1 inhibitor therapy. Pts received IVO 500 mg QD orally on days 1–28 of 28-day cycles. Results: As of 08May2021, 16 pts with R/R MDS were enrolled: 5 (31%) pts remained on treatment and free from leukemic transformation; 11 (69%) had discontinued including 6 for disease progression, 1 for allogeneic stem cell transplantation, and 1 owing to an adverse event (AE) of sepsis (the only fatal AE; reported by investigator as not related to IVO). AEs are summarized in the Table. 2 pts each experienced differentiation syndrome (grade 2) and QTcF prolongation (grade 1 and 2). 7/16 pts achieved complete response (CR, 44%; 95% CI, 20%, 70%), 1 achieved partial response (6%), and 5 achieved marrow CR (31%), resulting in an ORR of 81% (95% CI, 54%, 96%). Hematologic improvement in ≥1 lineages was achieved by 11/16 (69%) pts. The Kaplan-Meier estimate of duration of CR+PR at 12 months was 60%. 3 pts experienced CRs lasting 24.0, 63.7, and 65.4 months, which remain ongoing. 5/7 pts (71%) who were transfusion dependent at baseline became independent of red blood cell or platelet transfusions for 56 or more consecutive days on treatment. Additional translational data are being analyzed. Conclusions: In pts with m IDH1 R/R MDS, IVO monotherapy was tolerable and induced durable remissions and transfusion independence. These findings support the role of IVO as an effective, oral, targeted treatment for pts with m IDH1 R/R MDS. Clinical trial information: NCT02074839. [Table: see text]

Abstract BACKGROUND: Recurrent isocitrate dehydrogenase (IDH) 1 mutations are observed in 6-10% of patients with acute myeloid leukemia (AML). Ivosidenib (AG-120), a potent, selective, oral, small-molecule inhibitor of the mutant IDH1 (mIDH1) protein, is a promising therapeutic candidate for the treatment of patients with mIDH1 AML. Through inhibition of mIDH1, ivosidenib suppresses the abnormal production of the oncometabolite 2-hydroxyglutarate (2-HG), leading to clinical responses via differentiation of malignant cells. AIM: To report safety and efficacy data from the first-in-human phase 1 study of ivosidenib in patients with mIDH1 advanced hematologic malignancies including relapsed/refractory (R/R) AML (NCT02074839). This is the first report of data from the 4 expansion cohorts, with a total of 258 patients treated on study. METHODS: The ongoing phase 1 study assesses the safety, maximum tolerated dose (MTD), pharmacokinetics, pharmacodynamics, and clinical activity of ivosidenib in mIDH1 hematologic malignancies. Enrollment was completed on May 8, 2017. During dose escalation, patients received ivosidenib as a single agent orally once daily (QD) or twice daily (BID) in 28-day cycles. The MTD was not reached and 500 mg QD was selected as the recommended dose to be tested in 4 expansion cohorts: R/R AML (Arms 1 and 4, where Arm 1 patients are those with relapse after transplantation, second or later relapse, resistance to initial induction or reinduction treatment, or relapse within 1 year of initial treatment, and Arm 4 patients have R/R AML but are not eligible for Arm 1); untreated AML (Arm 2); and other advanced hematologic malignancies including myelodysplastic syndrome (MDS) (Arm 3). Updated safety data will be presented for all patients. Efficacy outcomes will be presented for all R/R AML patients treated at 500 mg QD across the dose escalation and expansion cohorts who received their first dose of ivosidenib at least 6 months prior to the analysis cut-off date of May 12, 2017, as well as for the poorest prognosis Arm 1 subset. Efficacy data for all treated patients from the other expansion cohorts (untreated AML and other advanced hematologic malignancies including MDS) will also be presented. RESULTS: In all, 258 patients (78 in dose escalation, 180 in expansion) were treated with ivosidenib. As of May 12, 2017, 62 of 258 (24%) patients were continuing on treatment. The median duration of exposure to ivosidenib was 3.5 months (range 0.1-33.5). Twenty-two (8.5%) patients discontinued treatment to proceed to allogeneic stem cell transplantation. Treatment was well tolerated; the most common adverse events (AEs) (n=258) of any grade irrespective of causality occurring in ≥20% of patients were diarrhea (33%), leukocytosis (30%), nausea (30%), fatigue (29%), febrile neutropenia (25%), dyspnea (24%), anemia (23%), QT prolongation (23%), peripheral edema (22%), pyrexia (21%), and decreased appetite (20%). The majority of these AEs were grades 1-2 and reported as unrelated to treatment. Differentiation syndrome (DS) was observed in 29 of 258 (11.2%) patients, including grade ≥3 DS in 14 (5.4%); study drug was held owing to DS in 11 patients (4.3%), and no instances of DS led to permanent treatment discontinuation or death. The primary efficacy endpoint for R/R AML is the CR+CRh rate, i.e., the rate of complete remission (CR according to modified IWG 2003 criteria plus CR with partial hematologic recovery, defined as CR except absolute neutrophil count >0.5 × 109/L [500/µL] and platelet count >50 × 109/L [50,000/µL]). Among 125 Arm 1 R/R AML patients receiving ivosidenib 500 mg QD across dose escalation and expansion who received their first dose at least 6 months prior to the analysis cutoff date, the CR+CRh rate was 30.4% (95% CI 22.5%, 39.3%), including CR in 27 (21.6%) and CRh in 11 (8.8%) patients. Median duration of CR+CRh was 8.2 months (95% CI 5.5, 12.0), and duration of CR was 9.3 months (95% CI 5.6, 18.3). The overall response rate (CR+CRi/CRp+PR+MLFS) was 41.6% (95% CI 32.9%, 50.8%) (52/125 patients). CONCLUSION: Ivosidenib monotherapy is well tolerated in patients with mIDH1 AML and other advanced hematologic malignancies. In a high-risk, molecularly defined R/R AML patient population with unmet medical need, ivosidenib induced durable remissions and improved patient outcomes. These findings support the role of ivosidenib as an effective, oral, targeted treatment for patients with mIDH1 AML. Disclosures DiNardo: Celgene: Honoraria, Research Funding; AbbVie: Honoraria, Research Funding; Agios: Honoraria, Research Funding; Daiichi-Sankyo: Honoraria, Research Funding; Novartis: Honoraria, Research Funding. De Botton: Pfizer: Honoraria; Novartis: Honoraria; Celgene: Honoraria; Servier: Honoraria; Agios: Honoraria, Research Funding. Stein: GSK: Other: Advisory Board, Research Funding; Constellation Pharma: Research Funding; Seattle Genetics: Research Funding; Agios Pharmaceuticals, Inc.: Consultancy, Research Funding; Celgene Corporation: Consultancy, Other: Travel expenses, Research Funding; Pfizer: Consultancy, Other: Travel expenses; Novartis: Consultancy, Research Funding. Roboz: AbbVie, Agios, Amgen, Amphivena, Array Biopharma Inc., Astex, AstraZeneca, Celator, Celgene, Clovis Oncology, CTI BioPharma, Genoptix, Immune Pharmaceuticals, Janssen Pharmaceuticals, Juno, MedImmune, MEI Pharma, Novartis, Onconova, Pfizer, Roche Pharmace: Consultancy; Cellectis: Research Funding. Mims: Novartis: Honoraria. Pollyea: Takeda, Ariad, Alexion, Celgene, Pfizer, Pharmacyclics, Gilead, Jazz, Servier, Curis: Membership on an entity's Board of Directors or advisory committees; Agios, Pfizer: Research Funding. Altman: Syros: Consultancy; NCCN: Other: Educational speaker; BMS: Consultancy; Celgene: Consultancy; Astellas: Consultancy; Ceplene: Consultancy; Janssen Pharmaceuticals: Consultancy; Novartis: Consultancy; ASH: Other: Educational speaker. Collins: Celgene Corporation: Research Funding; Agios: Research Funding; Arog: Research Funding; BMS: Research Funding. Mannis: Curis: Honoraria; Juno: Research Funding; Agios: Research Funding; Amgen: Honoraria. Uy: GlycoMimetics: Consultancy; Novartis: Consultancy, Other: Travel Suppport; Boehringer Ingelheim: Consultancy. Fathi: Juno: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Pfizer: Honoraria; Celgene: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Takeda: Research Funding; Agios: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Medimmune: Consultancy, Membership on an entity's Board of Directors or advisory committees; Amgen: Consultancy, Membership on an entity's Board of Directors or advisory committees. Stein: Amgen: Consultancy, Speakers Bureau; Stemline: Consultancy. Erba: Celgene: Consultancy, Other: Chair, Scientific Steering Committee , Speakers Bureau; Incyte: all research support paid to University of Alabama, Consultancy, Speakers Bureau; Jazz: Consultancy, Speakers Bureau; Novartis: Consultancy, Speakers Bureau; Amgen: Consultancy, Other: all research support paid to University of Alabama, Research Funding; Daiichi Sankyo: Consultancy, Other: all research support paid to University of Alabama, Research Funding; ImmunoGen: Consultancy, Other: all research support paid to University of Alabama, Research Funding; MacroGen: Consultancy; Ono: Consultancy; Pfizer: Consultancy; Seattle Genetics: Consultancy, Other: all research support paid to University of Alabama, Research Funding; Sunesis: Consultancy; Millennium/Takeda: Consultancy, Other: all research support paid to University of Alabama, Research Funding; Agios: Other: all research support paid to University of Alabama, Research Funding; Juno: Other: all research support paid to University of Alabama, Research Funding; Astellas: Other: all research support paid to University of Alabama, Research Funding; Celator: Other: all research support paid to University of Alabama, Research Funding; Janssen: Other: all research support paid to University of Alabama, Research Funding; Glycomimetics: Other: Chair, Data and Safety Monitoring Committee. Traer: ImmunoGen: Consultancy; Tolero: Consultancy; Notable Labs: Equity Ownership. Stuart: Pharmacyclics LLC, an AbbVie Company: Research Funding; Amgen: Consultancy, Honoraria; Agios: Research Funding; Celator/Jazz: Research Funding; Sunesis: Consultancy, Honoraria, Other: Travel Support, Research Funding; Bayer: Research Funding; Novartis: Research Funding; Incyte: Research Funding; ONO: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Research Funding; MedImmune: Research Funding; Cantex: Research Funding; Astellas: Research Funding. Arellano: Cephalon Oncology: Research Funding. Sekeres: Celgene: Membership on an entity's Board of Directors or advisory committees. Yen: Agios: Employment, Equity Ownership. Kapsalis: Agios: Employment, Equity Ownership. Liu: Agios Pharmaceuticals, Inc.: Employment, Equity Ownership. Goldwasser: Agios: Employment, Equity Ownership. Agresta: Agios Pharmaceuticals, Inc.: Employment, Equity Ownership. Attar: Agios: Employment, Equity Ownership. Stone: Novartis: Consultancy; Celgene: Consultancy; Amgen: Consultancy; Abbvie: Consultancy; Fuji Film: Consultancy; Jazz: Consultancy; Astellas: Consultancy; Pfizer: Consultancy; Arog: Consultancy; Ono: Consultancy; Agios: Consultancy; Sumitomo: Consultancy. Kantarjian: ARIAD: Research Funding; Bristol-Meyers Squibb: Research Funding; Delta-Fly Pharma: Research Funding; Amgen: Research Funding; Pfizer: Research Funding; Novartis: Research Funding.

Abstract BACKGROUND: Recurrent mutations in isocitrate dehydrogenase 1 (IDH1) are observed in approximately 4% of patients with myelodysplastic syndrome (MDS) and have been linked with increased transformation to acute myeloid leukemia. Ivosidenib (AG-120), an oral, potent, targeted, small-molecule inhibitor of the mutant IDH1 protein (mIDH1), is a therapeutic candidate for the treatment of patients with mIDH1 MDS. Through inhibition of mIDH1, ivosidenib suppresses the production of the oncometabolite 2-hydroxyglutarate (2-HG), leading to clinical responses via differentiation of malignant cells. AIM: To report safety and efficacy data from patients with relapsed or refractory (R/R) MDS enrolled in the first-in-human, phase 1, dose escalation and expansion study of ivosidenib in patients with mIDH1 advanced hematologic malignancies (NCT02074839). METHODS: This ongoing study is evaluating the safety, maximum tolerated dose (MTD), pharmacokinetics, pharmacodynamics, and clinical activity of ivosidenib. Trial enrollment was completed on 08May2017. In dose escalation, patients received single-agent ivosidenib orally once daily (QD) or twice daily in 28-day cycles. The MTD was not reached and 500 mg QD was selected as the dose to be tested in expansion. Expansion Arm 3 enrolled patients with mIDH1 advanced hematologic malignancies, including MDS. The overall response rate (ORR) for MDS was defined as complete remission (CR) + partial remission + marrow CR. Exploratory biomarker assessments included baseline co-occurring mutations (next-generation sequencing panel for hematologic malignancies) and mIDH1 variant allele frequency (VAF) in bone marrow mononuclear cells (BEAMing Digital PCR; lower limit of detection for mIDH1, 0.02-0.04%). Here, we present safety and efficacy data for patients with MDS in expansion Arm 3 and in dose escalation whose starting dose was 500 mg QD. RESULTS: In all, 258 patients (78 in dose escalation, 180 in expansion) received ivosidenib, including 12 patients with MDS (9 from expansion and 3 from escalation) whose starting dose was 500 mg QD. Baseline characteristics for these 12 patients were: 9 men/3 women; median age, 72.5 years (range, 52-78) and 42% were ≥75 years of age; median number of prior therapies, 1 (range, 1-3). As of 10Nov2017, 7 of 12 (58.3%) patients remained on treatment and 5 (41.7%) had discontinued (one for allogeneic stem cell transplantation). The median duration of exposure to ivosidenib was 11.0 months (range, 3.3-31.1). The most common adverse events (AEs) of any grade, irrespective of causality, occurring in ≥20% of the 12 patients were back pain (n=4, 33.3%) and anemia, decreased appetite, diarrhea, dyspnea, fatigue, hypokalemia, pruritus, and rash (n=3, 25.0% each). The majority of these AEs were grade 1-2 and reported as unrelated to treatment. No AEs led to permanent discontinuation of treatment. IDH differentiation syndrome (IDH-DS) was observed in 2 of 12 (16.7%) patients; the events were grade 1 and 2, respectively. Of the 12 patients with MDS receiving ivosidenib 500 mg QD, 5 achieved CR (41.7%; 95% CI 15.2%, 72.3%) and 6 achieved marrow CR (50.0%), resulting in an ORR of 91.7% (95% CI 61.5%, 99.8%). The median durations of CR and overall response were not estimable at the time of the data cutoff. The percentages of patients who remained in CR and response at 12 months were 60.0% and 61.4%, respectively. Among 5 patients who were transfusion dependent at baseline, 4 became transfusion independent for at least 56 days on treatment. Baseline co-occurring mutations and changes in mIDH1 VAF levels on ivosidenib therapy will be presented. CONCLUSION: In patients with mIDH1 R/R MDS, ivosidenib monotherapy was well tolerated and induced durable remissions and transfusion independence. These findings support the role of ivosidenib as an effective, oral, targeted treatment for patients with mIDH1 R/R MDS. Disclosures DiNardo: Karyopharm: Other: Advisory role; Medimmune: Other: Advisory role; Celgene: Other: Advisory role; Bayer: Other: Advisory role; Agios: Consultancy, Other: Advisory role; AbbVie: Consultancy, Other: Advisory role. Watts:Jazz Pharma: Consultancy, Speakers Bureau; Takeda: Research Funding. Stein:Celgene: Consultancy; Daiichi Sankyo: Consultancy; Agios: Consultancy; Pfizer: Consultancy; Novartis: Consultancy; Bayer: Consultancy. de Botton:Agios: Research Funding; Celgene: Honoraria, Research Funding. Fathi:Takeda: Consultancy, Honoraria; Jazz: Honoraria; Celgene: Consultancy, Honoraria, Research Funding; Boston Biomedical: Consultancy, Honoraria; Astellas: Honoraria; Seattle Genetics: Consultancy, Honoraria; Agios: Honoraria, Research Funding. Stein:Amgen: Speakers Bureau; Celgene: Speakers Bureau. Foran:Agios: Research Funding; Xencor, Inc.: Research Funding. Stone:AbbVie: Consultancy; Agios: Consultancy, Research Funding; Cornerstone: Consultancy; Orsenix: Consultancy; Fujifilm: Consultancy; Sumitomo: Consultancy; Pfizer: Consultancy; Celgene: Consultancy, Other: Data and Safety Monitoring Board, Steering Committee; Ono: Consultancy; Novartis: Consultancy, Research Funding; Otsuka: Consultancy; Jazz: Consultancy; Merck: Consultancy; Astellas: Consultancy; Arog: Consultancy, Research Funding; Argenx: Other: Data and Safety Monitoring Board; Amgen: Consultancy. Patel:France Foundation: Honoraria; Dava Oncology: Honoraria; Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Tallman:Cellerant: Research Funding; BioSight: Other: Advisory board; ADC Therapeutics: Research Funding; AbbVie: Research Funding; Daiichi-Sankyo: Other: Advisory board; AROG: Research Funding; Orsenix: Other: Advisory board. Choe:Agios: Employment, Equity Ownership. Wang:Agios: Employment, Equity Ownership. Zhang:Agios: Employment, Equity Ownership. Dai:Agios: Employment, Equity Ownership. Fan:Agios: Employment, Equity Ownership. Yen:Agios: Employment, Equity Ownership. Kapsalis:Agios: Employment, Equity Ownership. Hickman:Agios: Employment, Equity Ownership. Agresta:Agios: Employment, Equity Ownership. Liu:Agios: Employment, Equity Ownership. Wu:Agios: Employment, Equity Ownership, Patents & Royalties. Attar:Agios: Employment, Equity Ownership.

Background:Mutations in isocitrate dehydrogenase 1 (IDH1) occur in ∼4% of patients with myelodysplastic syndrome (MDS) and have been linked with increased transformation to acute myeloid leukemia (AML). Ivosidenib (IVO; AG‐120) is an oral, potent, targeted inhibitor of the mutant IDH1 protein (mIDH1) that is approved for the treatment of adults with mIDH1 relapsed or refractory (R/R) AML. Through inhibition of mIDH1, IVO suppresses production of the oncometabolite 2‐hydroxyglutarate, leading to clinical responses via differentiation of malignant cells.Aims:To report safety and efficacy data from patients with R/R MDS enrolled in the first‐in‐human, phase 1, dose escalation and expansion study of IVO in patients with mIDH1 advanced hematologic malignancies (NCT02074839).Methods:This ongoing study is evaluating the safety, maximum tolerated dose (MTD), pharmacokinetics, pharmacodynamics, and clinical activity of IVO. Enrollment was completed on May 8, 2017. In dose escalation, patients received single‐agent IVO orally (dose range, 200–1200 mg daily) in 28‐day cycles. The MTD was not reached and 500 mg QD was selected as the dose for expansion. The overall response rate (ORR) for MDS was defined as complete remission (CR) + partial remission + marrow CR (mCR) according to International Working Group 2006 criteria for MDS. Exploratory biomarker assessments included baseline co‐occurring mutations (next‐generation sequencing panel for hematologic malignancies) and mIDH1 variant allele frequency (VAF) in bone marrow mononuclear cells (BEAMing Digital PCR; lower limit of detection for mIDH1, 0.02–0.04%).Results:Baseline characteristics of the 12 patients with R/R MDS who received 500 mg IVO once daily were: 9 men/3 women; median age 72.5 years (range 52–78), and 42% were ≥75 years of age; median number of prior therapies 1 (range 1–3). As of Nov 2, 2018, 3 of 12 (25.0%) patients remained on treatment; 9 (75.0%) had discontinued (one for allogeneic stem cell transplantation). Median duration of exposure to IVO was 11.4 months (range 3.3–42.5). Adverse events (AEs) of any grade, irrespective of causality, occurring in ≥20% of the 12 patients were diarrhea, fatigue, back pain, rash (n = 4 each, 33.3%), anemia, urinary tract infection, decreased appetite, hypokalemia, arthralgia, dyspnea, pruritus, and hypotension (n = 3 each, 25.0%). No AEs led to permanent discontinuation of treatment. IDH differentiation syndrome was observed in 1 of 12 (8.3%) patients (grade 2). Electrocardiogram QT prolonged was reported in 2 of 12 patients (17%; grade 1 in 1 patient and grade 2 in 1 patient). Five of 12 patients achieved CR (41.7%; 95% CI 15.2%, 72.3%), 1 achieved PR (8.3%), and 5 achieved mCR (41.7%), resulting in an ORR of 91.7% (95% CI 61.5%, 99.8%). The median duration of CR was not estimable (NE) at the time of datacutoff and the median duration of response was 21.4 months (95% CI 2.3, NE). At 12 months, 60.0% of patients remained in CR. Among 5 patients who were transfusion dependent at baseline, 4 became transfusion independent for ≥56 consecutive days on treatment. Baseline co‐occurring mutations and changes in mIDH1 VAF levels will be presented.Summary/Conclusion:In patients with mIDH1 R/R MDS, IVO monotherapy was well tolerated and induced durable remissions and transfusion independence. These findings support the role of IVO as an effective, oral, targeted treatment for patients with mIDH1 R/R MDS.