CKAP4 and esophageal squamous cell carcinoma: Recent studies have found that CKAP4 can be detected in the serum of HCC, pancreatic ductal adenocarcinoma, esophageal squamous cell carcinoma, and lung cancer patients (Li et al., 2016; Cheng et al., 2017; Yanagita et al., 2018; Kimura et al., 2019; Wang et al., 2019).