SPP1 and cancer: Indeed, OPN takes part in a broad range of physiological events (Sodek et al, 2000), such as bone (Reinholt et al, 1990; Giachelli and Steitz, 2000) and vascular (Shijubo et al, 2000) remodelling and tissue repair, as well as in pathological processes, like cell-mediated immunity, dystrophic calcification, coronary stenosis, wound healing and cancer metastasis (Denhardt et al, 2001).