FLT1 and neoplasm: At distant premetastatic sites, VEGFR-1 + HPCs upregulate the expression of the very late antigen-4 ligand, which specifically adheres to the newly synthesized fibronectin to establish a fibronectin-rich local microenvironment for cellular cluster formation.13 These studies revealed that BM-derived HPCs could help prepare the premetastatic site for tumor metastasis.