PGR and endometrial polyp: Studies have shown proliferative and secretory phase-dependent changes in both ER and PR expression in endometrial polyps (Taylor et al., 2003; Peng et al., 2009) and expression differences between premenopausal and postmenopausal women (McGurgan et al., 2006; Gul et al., 2010); this switch may explain the higher incidence of endometrial polyps observed following menopause (Nijkang et al., 2019).