PTK2 and osteosarcoma: Human pulmonary artery endothelial cells secrete CXCL1 [160], which activates the CXCR2-focal adhesion kinase (FAK)-PI3K-PKB-NF-κB pathway in osteosarcoma circulating tumor cells [156,160], causing an increase in vascular cell adhesion molecule-1 (VCAM-1) expression in osteosarcoma circulating tumor cells [156,160], which increases the adhesion of osteosarcoma circulating tumor cells to blood vessel walls in the lungs.