The Endometrial Collaborative Group
19 Gynecologic Pathologists recommended modified endometrial precancer nomenclature and criteria.
Mutter G, and The Endometrial Collaborative Group*. Endometrial
intraepithelial neoplasia (EIN): Will it bring order to chaos? Gynecol Oncol
2000; 76:287-290.
*Members of the Endometrial Collaborative Group (1999) include: (Australia)
Andrew G. Ostor; (Canada) Alex Ferenczy; (France) Christine Bergeron; (Great
Britain) Harold Fox, Michael Wells; (Netherlands) Jan P. A. Baak; (Norway) Anne
Orbo; (Spain) Francisco F. Nogales; (Taiwan) Ming-Chieh Lin; (USA) Debra A.
Bell, Christopher P. Crum, William C. Faquin, Nancy B. Kiviat, George L. Mutter,
Marisa R. Nucci, Ralph M. Richart, Mark H. Stoler, Fattenah A. Tavassoli,
William R. Welch
Abstract: The diagnosis of precancerous lesions of the endometrium
remains unstandardized because existing World Health Organization classification
categories do not correspond to distinctive biologic groups and are inadequately
supported by reproducible histopathologic criteria. A group of gynecologic
pathologists was convened to consider revised diagnostic classification and
criteria based on newly available information. We propose the terms endometrial
hyperplasia (EH), endometrial intraepithelial neoplasia (EIN), and
adenocarcinoma to define distinctive subgroups that are functionally relevant to
clinical management of patients with endometrial disease. Endometrial precancers
are collectively designated EIN in recognition of their monoclonal growth. At
present there is no effective strategy for constructive subdivision of EIN
lesions into grades or subgroups. EIN is to be distinguished from adenocarcinoma
and the diffuse hormonal changes of EH seen in anovulation. An archive of
genetically and morphologically classified endometrial precancers at
www.endometrium.org provides a resource for centralized review of the
histopathology of EIN lesions. A new architectural criterion for EIN diagnosis,
diminution of stromal volume to less than approximately half of the total sample
volume, will also assist in discriminating between EH and EIN. Implementation of
this proposal will bring diagnostic terminology into agreement with current
concepts of premalignant endometrial disease and facilitate more uniform patient
management.
Features of EIN, as designated by the Endometrial Collaborative Group
- Precancers should be placed in a single diagnostic category distinguished
by terms which will not be confused with benign hormonal effects.
- The term Endometrial Intraepithelial Neoplasia was selected because of
the evidence that precancers are monoclonal and thus, neoplastic. Has
parallels elsewhere in the
female genital tract.
- Criteria for EIN should include architectural diagnostic criteria. Volume
Percentage Stroma (VPS) and lesion size thresholds are candidates for
relevant criteria.
- Endometria which do not meet diagnostic criteria for EIN and display
the field effects of unopposed estrogen therapy need to be distinguished from EIN lesions.
Many pathologists will prefer to continue using other terms for anovulatory
endometria such as "disordered proliferative endometrium", or
simply "changes of anovulation."
- Indeterminate cases will remain in any classification system, and the
pathologists opinion about confounding factors should be conveyed in the
report (e.g., sampling error, progestin therapy, non-endometrioid
differentiation).
