FLT1 and neoplasm: Kaplan et al. (2005) demonstrated that the migration of VEGFR-1-expressing bone marrow-derived hematopoietic progenitor cells (BMDCs) into organ-specific pre-metastatic sites was induced by tumor-derived conditioned media and that BMDC cluster formation, which create a favorable microenvironment for incoming tumor cells, preceded tumor cell arrival [166].