S100A9 also known as Calgranulin B, MRP14 is a member of the S100 family of proteins containing 2 EF-hand calcium-binding motifs. S100A9 plays a crucial role in the inflammatory response and cellular calcium signaling. S100A9 is primarily expressed in myeloid cells, such as macrophages and neutrophils, and is involved in various physiological processes, including the regulation of cell proliferation and differentiation. S100A9′s ability to bind calcium ions is essential for its function, as this binding influences the activity of other proteins and cellular pathways, making S100A9 a significant marker in studies related to inflammation and immune responses. S100A9 has been implicated in various pathological conditions, including cancer and autoimmune diseases, highlighting S100A9′s importance as a target for therapeutic interventions and diagnostic applications.