DKK1 and gastric cancer: DKK1 had decreased expression in both gastric cancer (GC) and colorectal cancer (CRC), but increased expression in breast cancer (BRCA) and non-small cell lung cancer (NSCLC) (Aguilera et al., 2006; Sato et al., 2007; Li et al., 2013; Jia et al., 2016; Kasoha et al., 2018).