S100A9 and cancer: Exosomes have been proposed to act as intercellular communicators between sender cells and receiver cells via complex cargo, including proteins, lipids, and nucleic acids.16 Researchers have elucidated the complex roles of exosomes in cancer progression.17 Exosomes from murine MDSCs carry biologically active molecules18 and play important roles in cancer progression.19 Especially, S100A9 was abundant in MDSC‐ derived exosomes.18 Although S100A9 was previously shown to up‐regulated in colorectal cancer, the relationship between MDSC exosomal S100A9 and colorectal cancer is unclear.