We demonstrate that breast cancer cell-derived factors can promote neutrophils to play a pro-tumor and pro-metastatic role through multiple mechanisms including upregulation of pro-tumor factors such as IL-1β, CCL2, CCL3, CCL4, IL23, and iNOS, NETosis, neutrophil survival longevity, and MMP9 secretion (Figure 7). Here, CCL3 is linked to breast cancer.