• Patient\* provides signed informed consent.

• Patient is ≥ 18 years at the time of given informed consent.

• Patient has histologically documented curatively resected intrahepatic cholangiocarcinoma, without metastatic spread, in the adjuvant situation (R0-resected)

• Patient has proven IDH1 mutation (IDH1-variant status evaluated locally by certified test on formalin-fixed paraffin-embedded tumor tissue specimen. If local testing for screening is not possible per local standard, tumor tissue samples will be subject to pre-screening via central IDH1 dPCR)

• Patient finished adjuvant systemic SOC chemotherapy (with regimens allowed per the protocol) directly prior to trial inclusion.

• Radiologic imaging available that shows that patient is tumor free at the timepoint of enrollment (not older than 6 weeks from the day of inclusion).

• Patient has ECOG Performance status ≤ 1

• Hematological, hepatic and renal function parameters adequate to allow targeted therapy with ivosidenib at investigator´s discretion and IB.

• Patient has adequate coagulability to allow targeted therapy with ivosidenib at investigator´s discretion and IB. Patients receiving warfarin / Phenprocoumon must be switched to low molecular weight heparin and before starting trial-specific.

⁃ Patient must be willingly to provide liquid biopsy samples, archival tumor tissue samples (if available), and in the event of disease recurrence, re-biopsy samples (if re-biopsy is considered safe for the patient) for the translational research program.

⁃ Female patients of childbearing potential or male patients with female partners of childbearing potential must agree to remain abstinent (refrain from heterosexual intercourse) or use contraceptive methods that result in a failure rate of \<1% per year during the treatment period and for at least 6 months after the last dose of trial treatment. Male patients with a pregnant partner must agree to remain abstinent or to use a condom for the duration of the pregnancy. Female patients of child-bearing potential must have a negative pregnancy test within the last 7 days prior to the start of trial therapy.

⁃ Patient is willing and able to comply with the protocol (including contraceptive measures) for the duration of the trial including undergoing treatment and scheduled visits and examinations including follow up.