Aberrant DNA methylation has been reported in endometriotic tissue in genes implicated in the hormonal and inflammatory factors of endometriosis pathogenesis (estrogen and progesterone receptors ERα, Erβ, and Prβ, the aromatase CYP19, the homebox protein HOXA-10, and the cyclooxygenase COX-2) [7,8,9,10,11,14]. The gene discussed is PGR; the disease is endometriosis.