PGR and endometriosis: Differentiation of endometriosis into two tissue types is reported to occur in a dual mode regulated by sex hormones [18, 19]: (1) estrogen and progesterone receptor-positive endometriosis lesions undergo malignant transformation to form hormone-dependent endometrioid carcinoma after long-term stimulation without antagonistic estrogen and (2) atrophic ectopic endometrial lesions negative for estrogen and progesterone receptors are stimulated by oxidative stress for a long period of time, resulting in malignant transformation and formation of non-hormone-dependent clear cell carcinoma.