Reproducibility of current classifications of endometrial endometrioid glandular proliferations: further evidence supporting a simplified classification

Aims To compare the reproducibility of the current (2003) W orld H ealth O rganization ( WHO ), endometrial intraepithelial neoplasia ( EIN ) and E uropean W orking G roup ( EWG ) classifications of endometrial endometrioid proliferations. Methods and results Nine expert gynaecological pathologists from E urope and N orth A merica reviewed 198 endometrial biopsy/curettage specimens originally diagnosed as low‐grade lesions. All observers were asked to classify the cases by using the categories described in each scheme: six for WHO , four for EIN , and three for EWG . The results were evaluated by kappa statistics for more than two observations. The analysis was repeated using only two major categories (benign versus atypical/carcinoma). Both the WHO and EIN classifications showed poor interobserver agreement ( κ  = 0.337 and κ  = 0.419, respectively), whereas the EWG classification showed moderate agreement ( κ  = 0.530). Full agreement between pathologists occurred in only 28% for the WHO classification, 39% for the EIN classification, and 59% for the EWG classification. With only two diagnostic categories, kappa values increased in all classifications, but only the EWG classification reached a substantial level of agreement ( κ  = 0.621); similarly, full agreement among all pathologists increased to 70% for the WHO classification, 69% for the EIN classification, and 72% for the EWG classification. Conclusions A two‐tier classification of endometrial endometrioid proliferative lesions improves reproducibility, and should be considered for the diagnosis of endometrial biopsy/curettage specimens.