CA9 and hepatocellular carcinoma: There is a broad spectrum of aggressive malignancies, where CA IX is predominantly overexpressed, namely, neuroblastoma (Ameis et al., 2016), breast tumor (Betof et al., 2012), head and neck tumors (Yang et al., 2014), ovarian tumor (Choschzick et al., 2011), pancreatic tumor (Couvelard et al., 2005), hepatocellular carcinoma (Huang et al., 2015), etc. In addition, there are several reviews, which summarize the significance of CA IX as a promising biomarker for the tumor development (Van Kuijk et al., 2016).