SPP1 and cancer: In murine endometrial cancer, forced expression of the CTHRC1 gene in cancer cells led to the appearance of M2 macrophages within the TME [105] and in the highly aggressive glioblastoma multiforme, expression of the ECM protein osteopontin is associated with adverse outcome and responsible for not only the recruitment of macrophages through a direct chemoattractant effect but also maintenance of macrophages in an M2 pro-tumourigenic state [134].