Pulmonary metastasis in breast cancer were further driven by CCL2-mediated recruitment of CD11b+ macrophages by primary tumor-induced fibrin clots.83 Mammary tumor-initiated pulmonary clots induce endothelial cell expression of vascular cell adhesion molecule 1 (VCAM1) and vascular adhesion protein 1 (VAP1) that tether macrophages. Here, CCL2 is linked to breast cancer.