PGR and endometriosis: In addition, some researches have found that the endometriotic tissue presented different expression patterns of DNA methylation compared with normal endometrium, and decreased expression of homeobox A10 (HOXA10) and progesterone receptor (PR) due to markedly elevated methylation at the promoter has been proven to contribute to the defective decidualization in the endometrium of endometriosis patients and induced endometriosis animals [14–17].