The Yokohama system for reporting directly sampled endometrial cytology: The quest to develop a standardized terminology.

BACKGROUND: The main purpose of directly sampled endometrial cytology is to detect invasive endometrial malignancies. With this principle in mind, The Yokohama System (TYS) Working Group, composed of cytopathologists, surgical pathologists, and gynecologic oncologists met at the 2016 International Congress of Cytology, Yokohama, with the aim to publish a standardized reporting system inclusive of specific diagnostic categories and cytomorphologic criteria for uniform and reliable diagnosis of endometrial malignancies on directly sampled endometrial samples.

METHODS: The diagnostic cytopathologic criteria previously published in the literature by the Japanese and Greek working group on endometrial cytology (Yanoh et al. [2012] Acta Cytol. 56:233; Margari et al. [2016] Diagn Cytopathol. 44:888-901) were critically reviewed with the aim of correlating the diagnostic classes to well defined risk categories for endometrial carcinoma (EC). Moreover, two classes of "atypical" endometrial cells were correlated respectively to a low- and high risk group. Some methodological suggestions for the application of ancillary special technologies to liquid based samples were also given.

RESULTS: The TYS group conceived a new Bethesda-style classification for directly sampled endometrial cytology which correlates the cytologic diagnostic classes with definite risk categories. The cytomorphologic findings have been correlated to the molecular pathology of EC, also through the application of ancillary special techniques to liquid-based samples.

CONCLUSIONS: The success of TYS will depend on the acceptance of TYS by all the relevant pathology and gynecologic oncology communities who, by their joint efforts, will adopt, critically evaluate, and optimize this method with the only aim of further improving the impact of endometrial cytology on patients' care.