Background & aims: Cholangiocarcinoma (CCA) is a rare cancer with limited therapeutic options and a poor prognosis. While first-line combination therapies have improved outcomes, second-line treatment remains challenging. Ivosidenib, an IDH1 inhibitor, has shown promise in treating IDH1 mutant CCA, but real-world data is limited. This study aims to evaluate ivosidenib's efficacy and safety in a large cohort of patients and compare it with second-line chemotherapy. Methods: This observational, retrospective, multicenter study included patients with advanced IDH1 mutant CCA treated with ivosidenib at 11 European institutions from May 2021 to September 2024. The primary endpoint was progression-free survival (PFS); the main secondary objectives were overall survival (OS), disease control rate (DCR), overall response rate (ORR) and safety. As a pre-planned exploratory objective, mPFS and OS of second-line ivosidenib and FOLFOX/CAPOX were compared by means of inverse probability of treatment weights (IPTW)-adjusted analysis. Results: The study included 46 patients treated with Ivosidenib; 43.5% received ivosidenib as second line and 56.5% as ≥ third line. Median PFS and OS were 3.7 (95% CI, 2.2-36.5) and 11.5 months (95% CI, 9.5-36.5). DCR was 50.0%. Grade ≥ 3 adverse events occurred in 8.7% of patients. IPTW-adjusted mPFS was 6.9 months with ivosidenib and 2.1 months with FOLFOX/CAPOX (HR: 0.36, 95% CI, 0.20-0.64, p = 0.0005), while the mOS was 15.9 and 9.0 months with ivosidenib and FOLFOX/CAPOX, respectively (HR: 0.47, 95% CI, 0.23-0.96, p = 0.0405). Conclusion: This study suggests that ivosidenib is a valid option for patients affected by metastatic IDH1 mutant CCA after at least one line of standard treatment
