A phase Ib/II study of olutasidenib in patients with relapsed/refractory IDH1 mutant solid tumors: Safety and efficacy as single agent.

e16643 Background: Isocitrate dehydrogenase 1 mutations (mIDH1) are present in a variety of solid tumors resulting in production and accumulation of (R)-2-hydroxyglutarate causing DNA hypermethylation and promoting tumorigenesis. Olutasidenib is an oral, potent and selective inhibitor of mutated IDH1 protein. We report preliminary results from the ongoing, first-in-human, Phase 1, open-label, single-arm study of olutasidenib in non-CNS solid tumors. Methods: Patients with advanced relapsed/refractory (R/R) mIDH1 solid tumors received olutasidenib 150 mg BID, orally. Following a dose confirmation cohort (Phase 1b), patients with intrahepatic cholangiocarcinoma (IHCC), chondrosarcoma (CS), or unspecified mIDH1 solid tumors (Other) were enrolled in a Phase 2 efficacy evaluation (NCT: 03684811). Results: As of 31-Oct-2019, 44 patients with relapsed or refractory mIDH1 solid tumors were treated with olutasidenib. Diagnosis included: IHCC (n = 26), CS (n = 13), and Other (n = 5). The median age was 58 years (range: 29-81) and 43% were male. Median number of prior treatments was 2 (1-10). mIDH1 status was locally determined (IHC, NGS or PCR): R132C (61%), R132G (7%), R132S (7%), R132H (2%), R132L (2%), Others (2%) & unspecified (18%). Fourteen patients discontinued treatment (disease progression [n = 6; 3 IHCC, 2 CS, 1 Other], AE [n = 4; 3 IHCC, 1 CS], PI decision [n = 3; IHCC] & withdraw consent [n = 1; IHCC]). Treatment emergent adverse events (all grades, regardless of attribution) that occurred in > 15% of pts were: nausea (43%), fatigue (25%), decreased appetite (22%), AST increase (18%), ALT increase (16%), and constipation (16%). No protocol-defined DLTs occurred. Best responses by tumor type are shown in the table. Conclusions: Single agent olutasidenib at 150 mg BID demonstrates acceptable safety and tolerability with preliminary clinical activity in patients with R/R mIDH1 solid tumors. Updated safety and clinical activity, as well as exploratory evaluations of PK/PD will be provided. Clinical trial information: 03684811 . [Table: see text]