Consistent with the immunohistochemical data from the PDX models of metastases, we also detected significant down-regulation of MFSD2A mRNA in CD31+ vascular endothelial cells fractionated from freshly resected human breast cancer brain metastases, as compared to CD31+ cells fractionated from adjacent non-cancerous brain tissue (Fig. 2F). Here, PECAM1 is linked to breast carcinoma.