Endometrial hyperplasia is believed to produce a continuum of lesions that may be precursor to endometrial carcinoma of endometrioid histology. The classification of endometrial hyperplasia has had numerous terminology. The classification below is currently the most commonly accepted system and is accepted by the World Health Organization (WHO) and the International Society of Gynecologic Pathologists. This system characterizes the glandular architectural pattern as simple or complex and describes the presence or absence of nuclear atypia.
Once a tissue diagnosis of endometrial hyperplasia is made, treatment depends on the patient's symptoms such as degree of bleeding, presence of cytologic atypia, patient's surgical risks, and wish for future childbearing. Progestins can effectively treat endometrial hyperplasia, and they can serve as prevention of recurrence in those with continued risk factors. Hyperplasia without atypia responds well to progestins. More than 98% of women with hyperplasia treated with cyclic progestins experienced regression of the disease in 3-6 months. The PEPI trial showed a 94% normalization of complex or atypical hyperplasia in 45 women treated with progestins. Multiple regimens of progestin therapy have been found effective in reversing hyperplasia.