DKK1 and CKAP4 were highly expressed in lung adenocarcinoma, pancreatic duct adenocarcinoma as well as esophageal squamous cell carcinoma and, apart from this, the synchronous expression of DKK1 and CKAP4 was correlated to a worse prognosis [6,31,111,112], while other CKAP4 ligands were not involved in cell proliferation of those cancers [6]. Here, DKK1 is linked to lung adenocarcinoma.