The elusive and controversial roles of estrogen and progesterone receptors in human endometriosis.

Endometriosis is a complex and challenging disease that involves aberrant adhesion, growth, and progression of endometrial tissues outside of the uterine cavity, and there is evidence to suggest that estrogen plays a key role in its development and progression. Numerous in vivo clinical studies have described the ectopic expression and regulation of estrogen receptor (ER) and progesterone receptor (PR) in the different types of endometriosis compared to normal or eutopic endometrium. However, we have noticed that conflicting and contradictory results have been presented in terms of ER subtype (ERα and ERβ) and PR isoform (PRA and PRB) expression. Both ER and PR are transcription factors and ER/PR-mediated responses depend on the coordinated, opposing, and compensatory functions of ER subtypes and PR isoforms. Moreover, analysis of the uterine phenotypes of ERα/ERβ and PRA/PRB knockout mice indicates that different ER subtypes and PR isoforms mediate distinct responses to steroid hormones and play different roles in uterine function. In this review, we outline studies that have elucidated the molecules and signaling pathways that are linked to ER and/or PR signaling pathways in the development and progression of endometriosis.