CLCA4 and pancreatic ductal adenocarcinoma: In addition, according to the literature, the mRNA levels of CLCA1 in colorectal cancer (Yang et al., 2013), ovarian cancer (Musrap et al., 2015), and pancreatic ductal adenocarcinoma (Hu et al., 2018) were different from those in normal tissues, and the loss of CLCA4 expression was observed in colorectal cancer (Chen et al., 2019), hepatocellular carcinoma (Liu et al., 2018), breast cancer (Yu et al., 2013), and bladder cancer (Hou et al., 2017).