Practical usefulness of atypical endometrial cell categories within the new classification of endometrial cytology when applied to conventional smears

Objective Endometrial cytology has been widely used as a screening tool in Japan. Traditionally, a three‐tier reporting system, consisting of ‘negative’, ‘suspicious’ and ‘positive’ categories, has been used. However, a more descriptive system, the New Terminology in Endometrial Cytology (NTEMC), which is based on the Bethesda System for uterine cervical cytology, was introduced recently. The objective of this study was to validate the NTEMC criteria. Methods Endometrial cytology specimens that had been categorised as ‘suspicious’ were collected in our hospital between 2003 and 2013, and from these, 106 specimens with corresponding histological results, were re‐evaluated according to the NTEMC criteria. Diagnostic categories were assigned based on that chosen by the majority of the examining members. Results Negative, atypical endometrial cells, of undetermined significance (ATEC‐US), atypical endometrial cells for which atypical endometrial hyperplasia or worse cannot be excluded (ATEC‐A), endometrial hyperplasia, atypical endometrial hyperplasia and malignancy were selected as the diagnostic categories for 9 (8.5%), 34 (32.1%), 17 (16%), 34 (32.1%), 5 (4.7%) and 7 (6.6%) specimens, respectively. Corresponding histological categories of benign, endometrial hyperplasia, atypical endometrial hyperplasia and malignancy were established in 28 (82.4%), 1 (2.9%), 2 (5.9%) and 3 (8.8%) ATEC‐US specimens, respectively, and in 6 (35.3%), 3 (17.6%), 2 (11.8%) and 6 (35.3%) ATEC‐A specimens, respectively. The histological category distribution differed significantly (P = 0.001), and there was a significant correlation between corresponding cytological and histological categories (P = 0.005). Conclusion The ATEC category of NTEMC system works well in a practical setting and resembles the Bethesda reporting system ASC (atypical squamous cells) category for cervical cytology. Descriptive new terminology in endometrial cytology has recently been introduced in Japan. Atypical endometrial cell categories including ATEC‐US (atypical endometrial cells of undetermined significance) and ATEC‐A (atypical endometrial cells for which atypical endometrial hyperplasia or worse cannot be excluded) worked well in a practical setting when these were correlated with histological categories.