CYP19A1 and endometriosis: Progesterone resistance resulting from dysregulation of aromatase and COX2 pathways in eutopic endometrial cells has been reported in women with endometriosis and is purported to negatively impact embryo implantation and/or facilitate peritoneal engraftment of shed cells in retrograde menstrual fluid (Giudice et al., 2002; Kao et al., 2003).