Endometrial hyperplasia is a medical condition which is characterized by abnormal thickening of the inner lining of the uterus. This is due to an excessive proliferation of the cells of the endometrium which predisposes the woman to tissue changes in the uterus. Endometrial hyperplasia initially represents a physiological response of endometrial tissue to the growth-promoting actions of estrogen. Nevertheless, the gland-forming cells of a hyperplastic endometrium may also undergo changes over time which predispose them to cancerous transformation.
Usually, endometrial hyperplasia result from high levels of estrogens, combined with insufficient levels of the progesterone-like hormones which ordinarily counteract estrogen's proliferative effects on this tissue. This may occur in a number of settings, including polycystic ovary syndrome, estrogen producing tumours and certain formulations of estrogen replacement therapy. Endometrial hyperplasia is a significant risk factor for the development of endometrial cancer so careful monitoring and treatment of women with this disorder is essential.