MDS-335: Ivosidenib (IVO) in Patients with IDH1-Mutant Relapsed/Refractory Myelodysplastic Syndrome (R/R MDS): Updated Enrollment for the MDS Sub-Study

Context: Mutations in isocitrate dehydrogenase 1 (IDH1) occur in ~3% of patients with MDS and are associated with increased transformation to acute myeloid leukemia (AML). IVO is an oral, potent, targeted inhibitor of the mutant IDH1 (mIDH1) enzyme and is FDA-approved for mIDH1 R/R AML and mIDH1 newly diagnosed AML in patients ≥75 years old or with comorbidities precluding the use of intensive induction chemotherapy. In the first-in-human, phase 1 study of IVO in patients with mIDH1 advanced hematologic malignancies (NCT02074839), 12 patients with R/R MDS, with median age 72.5 years (range 52–78), received IVO 500 mg once daily (QD). All patients received prior MDS treatment. Investigator-assessed ORR (CR + PR + marrow CR, per IWG 2006) was 75% (95% CI 43–95), with median duration of response of 21.4 months (95% CI 2.3–NE). Nine (75%) patients were transfusion-independent for ≥56 days during treatment. No dose-limiting toxicities or adverse events leading to treatment discontinuation were reported among patients with MDS. Based on these encouraging data, the FDA granted Breakthrough Therapy Designation to IVO in mIDH1 MDS; the study was amended to enroll additional patients with mIDH1 R/R MDS. Objective: To evaluate safety, tolerability, clinical activity, and pharmacokinetics/pharmacodynamics of IVO in patients with mIDH1 R/R MDS. Design: A sub-study of the single-arm, open-label, phase 1 dose escalation and expansion study of IVO in mIDH1 advanced hematologic malignancies, evaluating patients with R/R MDS. Patients must have R/R disease after prior standard therapy; high disease burden based on cytopenia and/or transfusion dependence at baseline; an Eastern Cooperative Oncology Group performance status score of 0–2; and be amenable to bone marrow aspirate and/or core biopsy at specified study timepoints. Patients with documented AML are not eligible. IVO 500 mg QD orally on days 1–28 of 28-day cycles. Results: Study is open; enrollment of ~23 patients from the US and France planned. Results not yet available. Conclusions: This sub-study will provide additional insights into safety, tolerability, clinical activity, and pharmacokinetics/pharmacodynamics of treatment with IVO in patients with mIDH1 R/R MDS. Funding: Agios; Servier.