SPP1 and cancer: OPN is detected in a wide range of tissues and body fluids, with physiological roles during development (e.g., in bone, bile duct formation, and during vascular remodeling), immune system regulation, and wound repair.3 However, it is also associated with pathological processes relating to cancer and inflammation.3, 4 The ability of OPN to mediate such diverse cellular functions is likely related to its extensive post-translational modifications and ability to signal through several integrin and CD44 variant receptors.3, 5