Endometrial intraepithelial neoplasia (EIN): Will it bring order to chaos?

The diagnosis of precancerous lesions of the endometrium remains unstandard ized because existing World Health Organization classification categories d o not correspond to distinctive biologic groups and are inadequately suppor ted by reproducible histopathologic criteria. A group of gynecologic pathol ogists was convened to consider revised diagnostic classification and crite ria based on newly available information. We propose the terms endometrial hyperplasia (EH), endometrial intraepithelial neoplasia (EIN), and adenocar cinoma to define distinctive subgroups that are functionally relevant to cl inical management of patients with endometrial disease. Endometrial precanc ers are collectively designated EIN in recognition of their monoclonal grow th. At present there is no effective strategy for constructive subdivision of EIN lesions into grades or subgroups. EIN is to be distinguished from ad enocarcinoma and the diffuse hormonal changes of EH seen in anovulation. An archive of genetically and morphologically classified endometrial precance rs at www.endometrium.org provides a resource for centralized review of the histopathology of EIN lesions. A new architectural criterion for EIN diagn osis, diminution of stromal volume to less than approximately half of the t otal sample volume, will also assist in discriminating between EH and EIN. Implementation of this proposal will bring diagnostic terminology into agre ement with current concepts of premalignant endometrial disease and facilit ate more uniform patient management. (C) 2000 Academic Press.