The colonization of new soil by metastatic seeds is a complex process, and a recent paper indicates that the education of stromal cells at a secondary site is important. Malanchi et al. show that the extracellular matrix component periostin (POSTN) is expressed by fibroblasts in the stroma of primary breast cancers. POSTN recruits WNT ligands and thereby increases WNT signalling in cancer stem cells. This expression of POSTN is required to allow cancer stem cell maintenance and to establish growth at a secondary site. Moreover, the development of metastases in the lung is reduced in Postn-null mice. Therefore, these authors conclude that cancer stem cells that successfully produce colonies at secondary sites do so by inducing stromal POSTN expression.