SPP1 and hepatocellular carcinoma: By analyzing the numbers of tumor-infiltrating immune cells and profiles of chemically induced liver tumors from WT and OPN-KO mice, OPN derived from host and HCC cells was found to stimulate macrophages to secrete CSF-1 and then activate the CSF1-CSF1R axis of macrophages to promote macrophage chemotaxis and M2-like polarization in HCC cells (18).