MMP9 and neoplasm: In the abovementioned studies, apelin treatment significantly increased tumor cell migration and invasion, and, moreover, it also induced the expression of several invasion and metastasis-related cytokines, e.g. matrix metalloproteinase-1 (MMP-1), matrix metalloproteinase-9 (MMP-9), interleukin-2 (IL-2) and interleukin-6 (IL-6)26,59,60.