S100A9 and cancer: The exact functional role of S100A9 in cancer and tumorigenesis is not entirely understood, but the protein acts upon immune and tumor cells to modulate the TME into an immunosuppressive state thereby promoting tumor progression and aggressiveness.[17, 52, 53, 54, 55] One hypothesis was that targeting S100A9 could block its function and delay tumor progression—however, S100A9‐targeted CCMV particles showed no efficacy even after lung homing (29–35% distribution).