Figure 1: Interactions between leukemic cells (lymphoblasts) and some of the BM components. Leukemic cells and endothelial cells produce vascular endothelial growth factor (VEGF), and basic fibroblast growth factor (bFGF) is produced by fibroblasts. VEGF plays a key role in vessel growth but also in blood vessel survival. Through its autocrine loop, VEGF enhances lymphoblast survival. The matrix metalloproteases secreted by lymphoblasts degrade the extracellular matrix and liberate growth factors such as bFGF. Hypoxia induces, via the HIF-1α subunit, the expression not only of VEGF but also of angiopoietin 2 (ANG). Endostatin (ES) is expressed by leukemic and stromal cells.