CCNB1 and endometriosis: As abundant expression of Cyclin B1 and alteration of the G2 pathway was reported in abnormal proliferative endometrial tissues, such as endometrial hyperplasia, endometrial adenocarcinoma and endometriosis[16,18,19,22-24] the down-regulation of cyclin B1 detected under the treatment of progesterone could well explain the underlying mechanism of the inhibitory effect of progesterone on endometrial cell growth.