CD44 and neoplasm: Circulating tumour cells express several ligands for E-, P- and L-selectins, including sLea, sLex and CD44, with ST3Gal enzymes most often implicated in their synthesis.114–117 Once circulating tumour cells have entered the bloodstream or lymphatic system, these selectin ligands help to tether the cells to the endothelium near the target organ prior to extravasation.