Cancer drugs that attack tumour-sustaining blood vessels may spur proliferation of the stem cells that contribute to the disease.

One such drug, bevacizumab, fails to prolong the survival of patients with advanced breast cancers, and studies have shown that patients on similar drugs often relapse. To find out why, Max Wicha and his team at the University of Michigan in Ann Arbor implanted human breast tumours into mice and treated them with bevacizumab and another blood-vessel-blocking drug, sunitinib. Treated tumours produced more cancer stem cells than untreated ones. The low-oxygen environment that the drugs create in tumours switches on a molecular pathway that encourages cancer stem cells to divide.

Combining these drugs with others that target cancer stem cells could yield a better outcome, the authors suggest.

Proc. Natl Acad. Sci. USA http://dx.doi.org/10.1073/pnas.1018866109 (2012)