Bleeding from an atrophic endometrium 36

Hormone replacement therapy (HRT) provides considerable advantages to women with respect to prevention of osteoporosis and protection from ischemic heart disease and stroke 1 . Conversely, there is a slight increased risk of breast carcinoma 2 and thromboembolic phenomena 3 . However, many women are persuaded against using HRT because of the continuation of regular menstrual bleeding with sequential combined regimens. In order to minimize this inconvenience, continuous regimens have been developed in which either combined regimens (Kliofem®) or single agents (tibolone) are used in order to prevent regular steroid withdrawal bleeding. Unfortunately between 15 and 25% of patients on these regimens continue to have endometrial bleeding 4 . These episodes of bleeding are reduced if HRT is begun after 1 year of amenorrhea and declines over the ist year of use. Why does this bleeding occur and why does it not occur in all patients?