FN1 and neoplasm: Adding even more complexity to the system, it has been shown in head and neck tumor cells that the multiprotein complex formed by α5β1-integrin, the urokinase receptor (uPAR) and their ligands fibronectin (FN) and uPA, induces a high and persistent activation of ERK, which is accompanied by tumor cell proliferation after recruitment and activation of EGFR [73,74].