DKK1 and breast cancer: Numerous studies have shown that Dickkopf WNT signaling pathway inhibitor 1 (DKK1), a secreted inhibitor of canonical Wnt signaling and osteoblast differentiation, was implicated in the migration and invasion of HCC, cholangiocarcinoma and breast cancer (Chen et al., 2013; Shi et al., 2013; Zhuang et al., 2017).