S100A9 and neoplasm: S100A9 expression has been found to correlate with acquired resistance to various cancer therapies, including targeted therapies (45), immunotherapy (46), chemotherapy (47), radiotherapy (48), as well as showing a complex relationship with prognosis, tumor mutational burden (TMB), microsatellite instability (MSI), DNA methylation, and immune cell infiltration across various tumor types (49).