CXCL12 and cancer: CXCL12 and its CXCR4 receptor play important roles in all phases of tumor progression, including cell proliferation and survival; the production of matrix metalloproteinases (MMPs) and invasion; the accumulation of cancer stem cells in the tumor; triggering functions related to metastasis such as epithelial-to-mesenchymal transition; promoting resistance to chemotherapy and endocrine therapy; and reducing the efficacy of immunotherapy [60].