It is interesting to note that the overexpression of ligands is not a rare event, since patients and cell lines resistant to bevacizumab (a VEGF blocking antibody) cause tumor cells to secrete additional angiogenic factors (FGF [167], PGF [168], members of the notch ligand/receptor family [169]) to compensate for the lack of VEGF signaling [170,171]. This evidence concerns the gene VEGFA and neoplasm.