MMP9 and melanoma: The enhanced transcription of MMP9 and ADAM9 observed in gray horse melanoma tissue is difficult to interpret, since the function of these proteases, at least in hMM, is site-dependent: There is evidence that MMP9 expression by hMM cells is associated with a pro-tumoral function, whereas stromal MMP9 expression seems to have an anti-tumoral effect [30,31].