Another important mechanism involved in GBM angiogenesis, apart from the migration and proliferation of the ECs, is the recruitment of pericytes and bone marrow-derived cells (monocytes, macrophages, and hematopoietic stem cells) in the perivascular tumor niche due to the activation of VEGFR-1 [152,154,155,156]. Here, FLT1 is linked to glioblastoma.