CXCR4 is a chemokine receptor known to highly express in MDA‐MB‐231 metastatic tumors.[qv: 12c,d] We confirmed that it is highly expressed in 231BR cells by flow cytometry (Figure3a) and in metastatic tumors in the brain by immunostaining (Figure 3b). Here, CXCR4 is linked to metastatic neoplasm.