Twist1 is a key inducer of epithelial-mesenchymal transition during tumor metastasis and is upregulated in aggressive human cancers. A new role for Twist1 in tumor progression was uncovered, showing that Twist1 is capable of stimulating angiogenesis via CCL2 production and subsequent recruitment of macrophages from the tumor stroma. Using a Matrigel plug assay, the images show that mouse mammary tumor cells endogenously expressing high levels of Twist1 stimulated a strong angiogenic response, seen as red blood vessels in the isolated plugs. When Twist1 expression was suppressed in these cells, the angiogenic response was diminished. For details, see the article by Low-Marchelli and colleagues on page 662.