MK and PTN are a two-member family of heparin-binding neurite outgrowth-promoting factors (39, 40), both of them can ligate with many receptors, such as syndecans (SDC3) (41, 42), integrins (ITGA6) (43), and nucleolin (NCL) (44), which help to promote neurite outgrowth and cell migration in a lot of inflammatory diseases and cancer. Here, MDK is linked to cancer.