Our recent study revealed for the first time that MMP-11 produced by macrophages enhanced the migration of HER2-positive breast cancer cells and recruitment of monocytes through C–C motif chemokine ligand 2 (CCL2)−CCR2 signaling, whereas MMP-11 overexpression in tumor cells did not promote the proliferation or migration of breast cancer cells (57). Here, MMP11 is linked to breast cancer.