DKK1 and cholangiocarcinoma: Likewise, high serum DKK1 levels make DKK1 a promising biomarker in esophageal squamous cell carcinoma, gastric cancer, pancreatic cancer, prostate cancer, cholangiocarcinoma, laryngeal squamous cell carcinoma, and HCC (Shi et al., 2013; Begenik et al., 2014; Rachner et al., 2014; Shi et al., 2014; Han et al., 2015; Liu et al., 2016a; Hong et al., 2018).