Neutrophils: Homing in on the myeloid mechanisms of metastasis

Highlights • Neutrophils play important roles throughout the metastatic process. • Tumour progression and invasion are influenced by infiltrating neutrophils. • Signalling from neutrophils can enhance survival of circulating tumour cells. • Neutrophils play a key role in establishing the metastatic niche.
The metastasis cascade is complex and comprises several stages including local invasion into surrounding tissue, intravasation and survival of tumour cells in the circulation, and extravasation and colonisation of a distant site. It is increasingly clear that these processes are driven not only by signals within the tumour cells, but are also profoundly influenced by stromal cells and signals in the tumour microenvironment. Amongst the many cell types within the tumour microenvironment, immune cells such as lymphocytes, macrophages and neutrophils play a prominent role in tumour development and progression. Neutrophils, however, have only recently emerged as important players, particularly in metastasis. Here we review the current evidence suggesting a multi-faceted role for neutrophils in the metastatic cascade.