MMP9 and neoplasm: Regarding the mechanism of action of MMPs on MICA/B, a few studies have reported that the secretion or expression of these metalloproteinases by tumor cells (including the secreted MMP-2, MMP-9 and MT-MMP-14) can lead to the proteolytic cleavage/shedding of MICA/B [45–51] and possibly ULBP2 and ULBP3 [60] at their surface.