The Yin/Yan of CCL2: A minor role in neutrophil anti-tumor activity in vitro but a major role on the outgrowth of metastatic breast cancer lesions in the lung in vivo

The role of the chemokine CCL2 in breast cancer is controversial. While CCL2 recruits and activates pro-tumor macrophages, it is also reported to enhance neutrophil-mediated anti-tumor activity. Moreover, loss of CCL2 in early development enhances breast cancer progression.