HIF1A and neoplasm: Furthermore, the HIF-1α and HIF-2α proteins become destabilized ex vivo in both EGFP+ and EGFP− tumor cells under the ambient tissue culture conditions (Additional file 2, pannel A), suggesting that the differential activation of the PI3K-AKT pathway that persists in cell culture after isolation from the xenografts is independent of HIF-1/2.