S100A6 and endometriosis: For example, total endometrial PGR expression and PR-A/PR-B expression ratio are critical for successful mammalian pregnancy as shown primarily in mice [16,17,18,19,20], but either PGR total expression or PR-A/PR-B ratios are dysregulated in the endometrium of many women with endometriosis [124,130,145,146,147,148].