MMP9 and endometriosis: Matrix metalloproteinases (MMPs), especially members of the group of gelatinases (MMP-2 and MMP-9), play a crucial role in the development of endometriosis, since MMP-9 has been shown to be increased in eutopic and ectopic endometrial tissue from women with endometriosis and higher levels of MMP-2, − 9, and − 14 mRNA have been found in endometriotic cells when compared to normal endometrium [5–7].