Metadherin (MTDH), also known as protein LYRIC or astrocyte elevated gene-1 protein (AEG-1), has emerged as an important oncogene protein that is overexpressed in all cancers analyzed so far. MTDH has been demonstrated to play a potential role in several significant aspects of tumor progression. The presence of the lung-homing domain of MTDH on tumor cells at the cell surface where it would be available to bind to vascular targets during metastasis has been confirmed. It has been reported that overexpression of MTDH is associated with the progression of the disease and a poorer prognosis in breast cancer. It has been reported that MTDH overexpression could significantly enhance the invasion and migration of breast cancer cells by inducing epithelial-mesenchymal transition (EMT) which is a process in which polarized epithelial cells are converted into motile mesenchymal cells. Thus, during cancer development, MTDH is conducive to tumor dissemination and metastatic spread.