SPP1 and breast cancer: Similarly, in human breast cancer, RUNX2 directly regulates the expression of MMP9 and MMP13 [16–18], bone sialoprotein and OPN [16], IL-8 [19] and the TGFβ-induced PTHrP levels [14] and mediates invasion of the human breast cancer cell lines MDA-MB-231 and MCF7 [17].