Interestingly, knockdown of endogenous HIF-1α by short-hairpin RNA in the cancer cells treated for 8 weeks impeded tumor growth but failed to prevent invasion, suggesting that intermittent induction of HIF1α(PP) in culture is key to programming glioma cells for invasion whereas endogenous HIF-1α potentially facilitates tumor growth. This evidence concerns the gene HIF1A and central nervous system cancer.