DDR1 and neoplasm: At molecular level, DDR1, PARD3, PARD6, CDH1, and CLDN11 are responsible for maintaining cell–cell junctions during cluster advancement [17,23]; PDPN, a mucin-like transmembrane protein frequently expressed in the leading edge of tumor, is implicated in guiding movement direction [24,25,26]; matrix metalloproteinases (MMPs) and basement membrane type IV collagens are required for track clearing and secondary ECM remodeling, respectively [27].