Nat. Med. 15, 1353 (2009); published online 4 December 2009; corrected after print 8 December 2009

In the version of this article initially published, the sentence “However, it failed in trials against early-stage colon cancers, and reports suggested that it might promote cancer metastasis in certain circumstances” was incorrect. Although it has been suggested that other strategies targeting blood vessel growth factors might promote tumor growth, this has not been specifically shown for Avastin. The text should read “However, it failed in trials against early-stage colon cancers. Reports have also suggested that targeting blood vessel growth factors might promote cancer metastasis in certain circumstances.” The error has been corrected in the HTML and PDF versions of the article.