Under continuous estrogen stimulation, the local endothelium does not respond properly to estrogen and progesterone or to progesterone, resulting in limited abnormal hyperplasia, which is manifested by varying degrees of hyperplasia and polyps, while the surrounding endothelium is often normal in shape. The increased incidence of endothelial polyps in perimenopausal women on hormone supplementation therapy can be attributed to this. Breast cancer patients are treated with tamoxifen after surgery. Tamoxifen prevents breast cancer recurrence by competitively binding to estrogen receptors in the breast to inhibit breast hyperplasia. However, tamoxifen may also exhibit estrogen agonist properties, so its long-term use may produce persistent trace estrogen-like effects on the endometrial lining and stimulate the development of endometrial polyps. The incidence of endometrial polyps in these patients increases with time to breast cancer onset, age at menopause, body mass index, and endometrial thickness.