RB1 and neoplasm: Though E7 oncoprotein expression in HPV-positive tumor cells was used in this study as a tool to bypass the G1-arrest, our data on HPV-negative tumor cells with an RB defect indicate that in genetically unstable cancer cells any pathway that can potentially lead to a premature G1/S transition and abolish the hypoxia-induced G0/G1-arrest will lead to a similar radiosensitivity phenotype upon reoxygenation, thus not limiting our findings to HPV-positive tumors.