In order to elucidate the effect of VEGF on A549 and SKMES1 lung cancer cells upon knockdown/blockade of all three VEGF receptors (NP1, NP2, KDR), a combined siRNA (NP1, NP2) and receptor blockade (KDR) approach was used (siCombo) in the presence or absence of VEGF. This evidence concerns the gene NRP1 and lung cancer.