This is a multicenter, single arm, open-label study in participants with unresectable BTC and disease progression or failure following one prior gemcitabine-based doublet chemotherapy regimen (combination of gemcitabine and cisplatin, or gemcitabine and other platinum agent/fluoropyrimidine agent). This study contains 3 phases: a Pre-treatment phase that will last within 21 days; a Treatment phase that will consist of study treatment cycles and tumor assessment conducted every 6-8 weeks; and a Follow-up phase that will begin immediately after the Off-Treatment Visit and will continue as long as the participant is alive, unless the participant withdraws consent, or until the End of Study.