Expression of the G protein-coupled estrogen receptor (GPER) in endometriosis: a tissue microarray study

A tissue microarray, which included 74 samples from different types of endometriosis (27 ovarian, 19 peritoneal and 28 deep-infiltrating) and 30 samples from normal endometrial tissue, was used to compare the expression levels of the GPER, estrogen receptor (ER)-alpha, ER-beta and progesterone receptor (PR). The immunoreactive score (IRS) was calculated separately for epithelium and stroma as the product of the staining intensity and the percentage of positive cells. The expression levels of the hormonal receptors were dichotomized into low (IRS？<？6) and high (IRS？>？=6) expression groups.The mean epithelial IRS (+/？standard deviation, range) of cytoplasmic GPER expression was 1.2 (+/？1.7, 0–4) in normal endometrium and 5.1 (+/？3.5, 0–12) in endometriosis (p？<？0.001), of nuclear GPER 6.4 (+/？2.6, 0–12) and 6.8 (+/？2.9, 2–12; p？=？0.71), of ER-alpha 10.6 (+/？2.4, 3–12) and 9.8 (+/？3.0, 2–12; p？=？0.26), of ER-beta 2.4 (+/？2.2; 0–8) and 5.6 (+/？2.6; 0–10; p？<？0.001), and of PR 11.5 (+/？1.7; 3–12) and 8.1 (+/？4.5; 0–12; p？<？0.001), respectively. The mean stromal IRS of nuclear GPER expression was 7.7 (+/？3.0; 2–12) in endometrium and 10.8 (+/？1.7; 6–12) in endometriosis (p？<？0.001), of ER-alpha 8.7 (+/？3.1; 2–12) and 10.6 (+/？2.4; 2–12; p？=？0.001), of ER-beta 1.8 (+/？2.0; 0–8) and 5.4 (+/？2.5; 0–10; p？<？0.001), and of PR 11.7 (+/？0.9; 8–12) and 10.9 (+/？2.0; 3–12; p？=？0.044), respectively. Cytoplasmic GPER expression was not detectable in the stroma of endometrium and endometriosis. The observed frequency of high epithelial cytoplasmic GPER expression levels was 50% (n？=？30/60) in the endometriosis and none (0/30) in the normal endometrium samples (p？<？0.001). High epithelial cytoplasmic GPER expression levels were more frequent in endometriomas (14/20, 70%; p？=？0.01), as compared to peritoneal (9/18, 50%) or deep-infiltrating endometriotic lesions (7/22, 31.8%). The frequency of high stromal nuclear GPER expression levels was 100% (n？=？74/74) in endometriosis and 76.7% (