The CXR4/CXL12 axis is also involved in the regulation of metastasis; indeed, chemokine receptors may intervene in each of the crucial steps of the metastasis mechanism to facilitate tumor progression, including tumor cell adhesion to the endothelium, extravasation from the blood vessels, metastatic colonization, angiogenesis, proliferation, and protection from host response through the activation of key survival pathways, such as ERK/MAPK, PI-3K/AKT/mTOR, or JAK/STAT. Here, MTOR is linked to neoplasm.