BMP4 and colorectal cancer: Among the five ligands that were found only in MC tissues, bone morphogenetic protein 4 (BMP4) (Lombardo et al., 2011), hyaluronic acid synthase 2 (HAS2) (Kim et al., 2019), and heparin-binding epidermal growth factor-like growth factor (HBEGF) (Yun et al., 2018) were reported to be involved in cell proliferation or cell migration in colorectal cancer.