More importantly, EMT serves as a critical biological step for endometriosis progression, because EMT results in a more aggressive capacity of the endometriotic cells (increased MMPs), leading to progesterone resistance (down-regulation of progesterone receptor) and triggering the formation of fibrosis (Zhang et al., 2016; Zondervan et al., 2018; Ma et al., 2021). Here, PGR is linked to endometriosis.