FLT1 and neoplasm: Moreover, bone marrow-derived VEGFR1-positive (VEGFR1+) hematopoietic progenitor cells (HPCs), in response to tumor-secreted growth factors and cytokines, may be recruited to distant organs to form clusters and create a permissive microenvironment that is structurally and functionally conducive to cancer metastasis [8, 9].