Endothelial cells form a phalanx to block tumor metastasis.

Tumor blood vessels deliver oxygen poorly, thereby contributing to tumor hypoxia and upregulation of proangiogenic cytokines in an escalating feedback loop. Mazzone et al. (2009) now show that reducing the amount of a protein involved in endothelial oxygen sensing leads to changes in endothelial cell shape that interrupt this feedback loop and reduce tumor metastasis.