CCL2 and breast neoplasm: To evaluate the capacity of CCL2 to entrain neutrophils to enhance tumor cell killing, we utilized a combination of in vitro experiments with exogenous delivery of CCL2 to co-cultures of neutrophils and either aggressive 4T1 breast cancer cells compared to a less aggressive 4T1 variant, 67NR, or co-cultures of neutrophils with either C576Bl/6 or FVB-PyMT breast tumor cells.