NANOG and ovarian endometriosis: Compared to normal endometrium, SOX2 protein expression in the eutopic and ectopic endometrium of ovarian endometriosis was significantly increased (P = 0.04; P = 0.009, respectively); NANOG protein expression in ectopic endometrium was statistically significantly different (P = 0.04); OCT4 protein expression in eutopic and ectopic endometrium tended to be higher (P > 0.05).