TCF21 and breast cancer: For example, re‐expression of TCF21 reduced cell growth and colony formation in lung cancer cells in vitro and in vivo (Smith et al., 2006), reduced cell proliferation, promoted apoptosis and suppressed cell invasion and migration in colorectal cancer in vitro (Dai et al., 2016), and reduced cell proliferation and epithelial–mesenchymal transition in breast cancer cells in vitro (Wang et al., 2015).