Neutrophils create a fertile soil for metastasis.

Neutrophils can facilitate the metastatic spread of cancer; however, how neutrophils are activated at metastatic sites remains poorly understood. In this issue, Xiao et al. demonstrate that the protease cathepsin C, secreted by breast cancer cells, triggers neutrophils to form neutrophil extracellular traps in the metastatic niche, thereby promoting lung metastasis.