Simple SummaryHuman epidermal growth factor receptor-2 (HER2) plays a critical role in breast and gastric cancer. More recently, a growing body of literature demonstrated that HER2 is involved in biliary tract cancers. In this review, we discuss the potential therapeutic utilization of HER2-blocking antibodies and ongoing clinical trials assessing the efficacy of HER2-blocking antibodies in HER2-altered and/or -amplified biliary tract cancers.AbstractDespite recent advances, biliary tract cancer (BTC) is traditionally known as being hard to treat with a poor prognosis. Recent state-of-the-art genomic technologies such as next-generation sequencing (NGS) revolutionized cancer management and shed light on the genomic landscape of BTCs. There are ongoing clinical trials to assess the efficacy of HER2-blocking antibodies or drug conjugates in BTCs with HER2 amplifications. However, HER2 amplifications may not be the sole eligibility factor for these clinical trials. In this review, we aimed to comprehensively examine the role of somatic HER2 alterations and amplifications in patient stratification and provide an overview of the current state of ongoing clinical trials.