Among them, cyclooxygenase 2 (COX2), matrix metalloproteinase 1 (MMP1) and matrix metalloproteinase 2 (MMP2) secreted by primary tumors were found to affect vascular integrity by changing the morphology of endothelial cells and improving vascular permeability in the lung metastasis model of breast cancer mice (25). Here, MMP2 is linked to breast cancer.