Idh1 Mutation Detection In Plasma Circulating Tumor Dna (Ctdna) And Association With Clinical Response In Patients With Advanced Intrahepatic Cholangiocarcinoma (Ihc) From The Phase Iii Claridhy Study.

4576 Background: Mutations in isocitrate dehydrogenase 1 ( IDH1) are detected in ~13% of IHCs. Ivosidenib (IVO) is a first-in-class, oral inhibitor of the mutant IDH1 (mIDH1) protein. In ClarIDHy, a global, phase 3, double-blind study in previously treated patients with advanced m IDH1 IHC (N = 186), IVO demonstrated an improvement in progression-free survival (PFS) vs placebo (hazard ratio 0.37, p < 0.001) (Abou-Alfa et al., Ann Oncol 2019; NCT02989857). Feasibility of m IDH1 detection in plasma ctDNA from patients with IHC was demonstrated and was highly concordant with mutation status in tumor tissue (Aguado-Fraile et al., Cancer Res 2019). This analysis was extended to the larger patient cohort from ClarIDHy, and longitudinal m IDH1 detection from ctDNA was assessed and correlated with clinical response. Methods: Baseline plasma and tumor tissue samples were obtained before randomization; longitudinal plasma samples were collected on day 1 of each treatment cycle. m IDH1 status in tissue was prospectively and centrally confirmed using Oncomine Focus Assay. A BEAMing digital PCR test was used for quantification of m IDH1 in plasma. IDH1 mutation clearance ( IDH1-MC) was achieved when plasma m IDH1 variant allele frequency was below the assay’s sensitivity (0.02% for R132C/L/S/G; 0.04% for R132H). Results: m IDH1 detection in plasma ctDNA and tissue was concordant in 92% (193/210) of samples screened. As of 31 Jan 2019, median PFS was 2.7 months for IVO vs 1.4 months for placebo. Longitudinal analysis with biomarker data available as of Jan 2020 demonstrated IDH1-MC in plasma from 10 IVO-treated patients with PFS ≥2.7 months (n = 36) vs 0 patients with PFS < 2.7 months (n = 40). No IDH1-MC was observed in patients treated with placebo, irrespective of response (n = 49). Conclusions: These results reinforce the feasibility of IDH1-R132 detection in plasma from patients with IHC, with a 92% concordance with detection in tumor tissue, supporting m IDH1 detection in liquid biopsy as a viable patient selection strategy where tissue exhaustion can limit conventional methods. Plasma IDH1-MC was also observed in a subset of IVO-treated patients who achieved disease control. Clinical trial information: NCT02989857 .