MMP9 and endometriosis: When comparing MMP-9 expression between ectopic endometrium in group 1 (with endometriosis) and eutopic endometrium in group 2 (control group), a significant difference between them was established (1.87 ± 0.30 IHC optical density score vs. 1.35 ± 0.06 in the control group, p < 0.001).