Clonogenic cell survival under hypoxia. (A) PC-3 cells were exposed to 1% oxygen for 0.5, 2, 6 or 24 h, prior to culturing them in an aerobic environment (21% oxygen) for 14 days. Cell colonies (> 50 cells) were counted macroscopically (6 wells/sample with 3 independent samples). N=normoxia; H=hypoxia. ***, p < 0.001 (n=18, Wilcoxon test). (B) Typical wells in A are shown.