In breast to lung cancer metastasis, a number of genes such as MMP1, MMP2, CXCL1, PTGS2, ID1, VCAM1, EREG, SPARC, and IL13RA2 have been identified in breast to lung cancer metastasis that promote and are clinically correlated; as well as the mitogen-activated protein kinases (MAPK), NFκB and vascular endothelial growth factor (VEGF) signaling pathways (111) (45). Here, MMP1 is linked to lung cancer.