SFRP1 and cancer: The Wnt-signalling pathway is an important activator of mouse mammary branching morphogenesis [37], and two further RNAs in our signature indicated an involvement of our PAFs in the activation of the Wnt-pathway and mammary stem cells: Postn and Sfrp1. Postn is necessary for correct collagen fibril assembly [38] and for metastatic colonisation, recruiting Wnt-ligands for cancer stem cell maintenance [39].