To clarify the role of miR-101-3p in the transmigration of BC cells trough the brain endothelium, we compared the expression profile of miR-101-3p in BC cell lines with those of PTGS2 (coding for COX-2), ST6GALNAC5 and HBEGF, three pro-metastasis genes known to mediate the transmigration of tumor cells through the BBB [17]. The gene discussed is PTGS2; the disease is breast cancer.