New WHO Classification of Endometrial Hyperplasias.

Deutschsprachige Zusatzinformationen online abrufbar unter: www.thieme-connect.de/ ejournals/toc/gebfra Endometrioid endometrial carcinoma, the most common form of endometrial cancer, usually develops out of a typical sequence of endometrial hyperplasias. The underlying cause of these hyperplasias is a relative predominance of estrogen combined with insufficient progesterone levels. Typical causes include corpus luteum insufficiency/anovulatory cycles (premenopause), polycystic ovary syndrome and obesity with metabolic syndrome (aromatase conversion of ovarian androgens in adipose tissue), inappropriate hormone therapy post menopause (insufficient dosage of gestagens) or an estrogen or androgen-producing tumor [1]. Even in patients with Lynch syndrome (formerly known as HNPCC), tumorigenesis of hereditary endometrioid carcinoma usually follows the usual progression with development of the respective hyperplasias [1]. Up to now, the correct clinical evaluation of endometrial hyperplasias was made more difficult by the different classification systems still in use: in Germany hyperplasias are sometimes still differentiated according to the classification “glandular-cystic hyperplasia” and “adenomatous hyperplasia grade I to III”. In 1994, the WHO classified endometrial hyperplasias into 4 categories: 1. simple hyperplasia without atypia, 2. complex hyperplasia without atypia, 3. simple atypical hyperplasia, 4. complex atypical hyperplasia [1,2]. While categories 1, 2 and 4 were generally accepted, pathologists continued to debate the existence of group 3-type hyperplasias. Hyperplasias without atypia (categories 1 and 2) are considered benign pathologies which will regress with conservative treatment (oral gestagens, gestagen IUD, elimination of the cause of anovulation/corpus luteum insufficiency) [1]. A large percentage (up to 60%) [3] of atypical endometrial hyperplasias (categories 3 and 4) are found to be coexistent with invasive endometrial carcinoma or develop