MAPK1 and endometriosis: Ngo et al. (2010) compared ectopic and eutopic endometrial cells from biopsies of patients with and without endometriosis, and observed that the MAPK pathway was activated in ectopic and eutopic endometrial cells from patients with endometriosis, as evidenced by a significantly higher pERK/ERK ratio in these patients compared to the control group [43].