MMP9 and nasopharyngeal carcinoma: Exosomes derived from NPC cells can significantly induce IL-6 production from macrophages, then, IL-6 significantly increased the malignant behaviors of NPC cells by regulating various oncogenic processes mediated by STAT3 or upregulating the expression of matrix metalloproteinase (MMP)-2 and MMP-9, thereby promoting NPC cells migration and invasion (19, 34, 70–72).