A 58-year-old postmenopausal woman on estro¬gen replacement complains of recent onset of spotting. A bimanual pelvic examination is unremarkable. Most likely diagnosis?

Any postmenopausal woman who has been on unop­posed estrogen and who is now experiencing vaginal bleeding is suspect for either endometrial hyperplasia or endometrial cancer. Endometrial hyperplasia is the end result of pro­longed estrogenic stimulation of the endometrial mu­cosa. Morphologic forms of hyperplasia include cystic, adenomatous, and atypical hyperplasia. In cystic hy­perplasia (simple hyperplasia), there are large, dilated glands lined by actively mitosing epithelial cells. Ade­nomatous hyperplasia refers to branching of the glands with papillary infolding or outpouchings (sometimes referred to as complex hyperplasia). Atypical hyperpla­sia has more glandular crowding and nuclear atypia than the latter condition and has the highest risk for progressing into carcinoma in situ and endometrial carcinoma. Endometrial carcinoma is the most common inva­sive cancer of the female genital tract. As with endome­trial hyperplasia, the risk factors for endometrial cancer primarily relate to hyperestrinism and include obesity, nulliparity, diabetes, hypertension, infertility, breast cancer, low fiber/high fat diet, early menarche or late menopause, and tamoxifen. The most common clini­cal presentation is vaginal bleeding (90%) in a post­menopausal woman.