Endometrial intraepithelial neoplasia (EIN) classification is proposed as a new diagnostic system to resolve the limitations of the World Health Organization (WHO) classification in routine practice. Our aim was to find out whether EIN classification excels the WHO classification regarding the accurate prediction of coexisting endometrial carcinomas (EC) in biopsy specimens. We retrospectively re-classified 139 WHO-classified endometrial hyperplasia (EH) cases by subjective EIN diagnosis and compared the incidence of coexisting carcinomas using two classification systems by re-evaluating biopsy and corresponding hysterectomy specimens. Of 139 WHO-classified hyperplasia cases, 36 and 103 were classified as benign and EIN cases, respectively. Forty of 93 cases with atypical EH had EC at hysterectomy as compared with 2/46 cases without atypical EH, while EC was detected in 42/103 cases with EIN, and in 0 of 36 cases without EIN. The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for atypical EH vs. non-atypical EH in biopsy specimen was 95.2%, 45.4%, 43.0% and 95.7%, respectively. For EIN vs. benign, the sensitivity was 100% and the specificity was 37.1%. The incidence of coexisting carcinomas in EIN cases was similar to that in atypical EH cases. However, regarding the exclusion of coexisting carcinomas, EIN criteria of benign lesions excelled the WHO criteria of non-atypical EH/CH.
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