The lining of the uterus, the endometrium, thickens in response to estrogen stimulation. In a pre-menopausal woman, the endometrium thickens in response to rising estrogen levels during the menstrual cycle, then sheds at the times of menses. An abnormally thickened endometrium in a postmenopausal woman generally requires further evaluation to rule out endometrial cancer. An endometrial biopsy is needed to determine whether the thickened endometrium is due to endometrial cancer. The pathologist will look at the endometrial tissue specimen under the microscope to determine whether the cells are normal, pre-cancerous (atypical endometrial hyperplasia), or cancerous. If the endometrial biopsy shows cancer, you should discuss with your doctor the option of referral to a gynecologic oncologist for further management.