Congruence between 1994 WHO classification of endometrial hyperplasia and endometrial intraepithelial neoplasia system

Objectives: To assess congruence between World Health Organization (WHO) 1994 and endometrial intraepithelial neoplasia (EIN) classification systems of endometrial hyperplasia. Methods: Systematic review and meta-analysis were performed by searching electronic databases for studies that classified endometrial hyperplasia according to both WHO 1994 and EIN systems. Congruence was based on the rate of specimens classified as EIN in WHO categories, which should be virtually 0.000 in nonatypical hyperplasia (NAH) and 1.000 in atypical hyperplasia (AH). Subgroup analyses were performed based on architecture complexity. Results: Eight studies with 1,352 hyperplasias were included. Congruence with EIN criteria was fair in NAH (0.241) and moderate in AH (0.815). Subgroup analyses of NAH showed high congruence in simple NAH (0.065), null in complex NAH (0.517), null in simple AH (0.148), and high in complex AH (0.901). Conclusions: WHO 1994 system is not congruent with the EIN system and cannot be directly translated into a dual classification.