SPP1 and cancer: SPP1 (Secreted Phosphoprotein 1/Osteopontin/OPN) is a chemokine-like matrix phosphoglycoprotein that not only affects cell proliferation and invasion, but is also involved in the invasive and metastatic processes of many cancers, and is considered as a prognostic and diagnostic marker for several cancers (Shevde and Samant, 2014).