Retraction of: Nature Published online 27 May 2015

The Editors have retracted this paper because, in their view, data in Extended Data Fig. 1d and Extended Data Fig. 4a are unreliable. Issues with the original antibody used in Extended Data Fig. 1d and 4a have been identified. The western blots showing an increase in secreted LOX in bone-trophic and hypoxic MDA-MB-231 cells, and shRNA knockdown of LOX in 4T1 cells, present unreliable bands. R.L. agrees with the retraction. All other authors disagree with the retraction and believe the findings are still valid.