Osteopontin 

Osteopontin (OPN) is a secreted, multifunctional, extracellular matrix (ECM), calcium-binding, glycosylated phosphoprotein that is associated with various normal biological functions and pathological processes. OPN is physiologically produced by a wide range of cells and has been identified in various body fluids, playing a crucial role in bone remodeling and vascularization. OPN is also expressed by multiple immune cells, acting as a chemotactic factor, a mediator of cell activation and cytokine production, and an anti-apoptotic factor, thereby regulating inflammation and immune responses. OPN can be involved in the tumorigenesis of various cancer types, including head and neck squamous cell carcinoma (HNSCC), by promoting cell proliferation, adhesion, invasion, and migration through multiple signaling pathways^[1][2].

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