For instance, He et al. found that 4T1 cells can penetrate the BBB and specifically adhere to sites of brain inflammation in the presence of brain metastasis through two pathways: (i) syndecan-1 (CD138) on the cell membrane can specifically interact with brain vascular endothelial cells, platelets that preferentially accumulate at sites of brain inflammation, and leukocytes (e.g. platelet endothelial cell adhesion molecule-1 (CD31) on monocytes and neutrophils; and (ii) VCAM-1 overexpressed on the membrane has high affinity for very late antigen 4 (VLA-4) on leukocytes. The gene discussed is PECAM1; the disease is brain inflammatory disease.