CXCL12 and nasopharyngeal carcinoma: SDF-1 (CXCL12) and its receptor, chemokine receptor 4 (CXCR4), play an important role in tumor cell proliferation, migration, adhesion, extracellular matrix degradation, angiogenesis, and immune tolerance induction [26], and CXCR4 expression is associated with a poor overall survival (OS) in NPC patients [27].