MMP2 and breast cancer: As shown in Figure 4, for example, MSC-derived exosomes play a role in transporting MMP-2 [41], miR-21, and miR-34a [36], which have been demonstrated to be involved in cancer cell survival [86] and proliferation [2, 87], and MMP-2, which has also been demonstrated to be overexpressed in breast cancer cells; additionally, the high expression of MMP-2 is associated with poor prognosis [88, 89].