However, several case reports have explored the potential of HER2-targeted therapy in biliary tract cancers (BTCs) (Bang et al. 2017; Javle et al. 2015; Nam et al. 2016), demonstrating objective response rates of 64% and 22% in HER2-positive BTC patients treated with HER2-targeted therapies in two phase II studies (Hainsworth et al. 2018; Hyman et al. 2018). Here, ERBB2 is linked to biliary tract cancer.