Many NRs have gained attention in stem cell biology (139–142); estrogen receptor (ERα), PR, and PPARγ are all implicated in endometriosis (143–146); and AR, thyroid receptor (TR), farnesoid X receptor (FXR), Rev-erb, and constitutive androstane receptor (CAR) are reported in tissue regeneration (147–152). Here, PGR is linked to endometriosis.