Endothelial progenitor cells (EPCs) are adult bone marrow derived vascular progenitors, which promote rapid blood vessel formation and tumor spread. Since they were proposed more than ten years ago, the role they play in controlling vascular development in a growing tumor and metastases has made them the subject of extensive study, and controversy1-3 . In recent years, it has become increasingly clear that not only do EPCs form a distinct vascular bone marrow derived lineage, but that their role in promoting adaptive resistance in tumors, following anti-angiogenic therapies, must be considered when designing future anti-cancer strategies. Using novel strategies in retroviral based delivery of transgenes we report for the first time on the characterization of a clinically significant/miRNA pathway regulating both EPC and tumor vascular biology. In work in review in Cancer Research4 , we also demonstrate the use of a strategy for the peptide directed delivery of liposome encapsulated anti-miRs, to modulate vascular miRNA signaling in situ, with consequent effects on tumor growth and vascularization.