Another relevant study characterizing CTCs from patients with advanced breast cancer identified cyclooxygenase COX2 (PTGS2), the epidermal growth factor receptor (EGFR) ligand HBEGF and the alpha2,6-sialyltransferase ST6GALNAC5 as key players for tumor cells to cross the blood-brain barrier (119). Here, EGFR is linked to breast carcinoma.