MMP9 and breast cancer: The inhibition of Slit2/Robo1 and therefore of the above-mentioned pathway leads to increased levels of MMP-9 in brain-selective breast cancer cells, suggesting the activity of the Slit2/Robo1 axis as an important parameter for brain metastasis in breast cancer patients, mediated via the PI3K/Akt/β-catenin/MMP-9 signaling pathway [72].