As positive staining for S100A4 occurs more often in advanced rather than in early breast cancers in contrast to the other three MIPs (de Silva Rudland et al, 2011; Winstanley and Rudland, 2013), it may be that only S100A4 has a role in the subsequent progression of those patients with BMs, whereas the other three MIPs stimulate earlier and different steps in the metastatic pathways. Here, S100A4 is linked to breast cancer.