Structure of the tumor cell glycocalyx. The glycocalyx is the first line of contact between the tumor cell and the components of the ECM such as fibronectin, collagens, and laminin. The cancer cell glycocalyx consists of four main glycan branches on four distinct types of protein or lipid backbone: O-glycans attached to glycoproteins and mucins at serine/threonine sites, N-glycans attached to glycoproteins at asparagine sites, gangliosides attached to ceramide glycolipids, and GAGs characterized by the Xyl-Glc-Glc motif attached to a protein at a serine/threonine site on proteoglycans.