MMP9 and breast cancer: Ly6C+ monocyte recruitment is driven by CCL2 secretion, promoting BC cell extravasation into the lung tissue via VEGFA and MMP9.168 Similarly, Gr-1 + CD11b+ myeloid lineages contribute by releasing MMP9, disrupting endothelial monolayers, and enhancing vascular permeability.169 Collectively, these studies highlight the role of neutrophils and classical monocytes in regulating endothelial permeability, facilitating cancer cell extravasation, and bone colonization (Fig. 3).