In the research of effect of 21 matrix metalloproteinases on brain metastasis‐free survival of breast cancer, only matrix metalloproteinase‐1(MMP‐1) is significantly correlated with BM.128 MMP‐1 has highly expressed in brain metastatic cells and is able to degrade claudin and occludin but not ZO‐1, which are critical factors of BBB. Here, MMP1 is linked to breast cancer.