CTSC and neoplasm: Neutrophils recruited to the site of metastasis have been shown to promote tumor progression such as a study that showed that the tumor‐secreted protease cathepsin C (CTSC) promotes metastasis from breast to the lung by enhancing the infiltration of neutrophils and the formation of neutrophil extracellular traps (NETs), which in turn promotes tumor cell extravasation and their colonization in the lungs.56