Another study revealed that miR-509 suppressed the invasion and trans-endothelial migration of brain metastatic TNBC cells by inhibiting Rho-mediated MMP-9 expression, and high MMP-9 gene expression is significantly associated with shorter brain-metastasis-free survival in breast cancer patients, indicating that miR-509/Rho/MMP-9 axis is a potential target of brain metastasis of breast cancer (46). The gene discussed is MMP9; the disease is breast cancer.