Pathological diagnosis of general rules for the description of thyroid cancer by Japanese Society of Thyroid Pathology and Japan Association of Endocrine Surgery

The Japanese Society of Thyroid Pathology and the Japan Association of Endocrine Surgeons developed the eighth edition of the General Rules for the Description of Thyroid Cancer (GRDTC) in December 2019. This article describes the pathological diagnosis of the GRDTC, which has been improved through repeated revisions based on the experience of Japanese pathologists and translated into English to introduce the Japanese diagnostic standard to foreign countries. In this edition of the GRDTC, the histopathological classification and descriptions differ in some respects from those of the fourth edition of the World Health Organization (WHO) classification as revised in 2017. For example, the GRDTC does not adopt the concept of borderline lesions (FT-UMP, WDT-UMP, and NIFTP) of the WHO, taking into consideration the popular histological criteria accepted by Japanese pathologists. The cytological reporting system of the GRDTC was partly modified from the Bethesda system in 2015. It has an additional cyst fluid category separated from the unsatisfactory category that has been demonstrated to be useful in Japan. This translated edition makes it easy to submit Japanese clinicopathological studies of thyroid tumors in an international journal. We also wish to contribute to the improvement, standardization, and globalization of the pathological diagnosis of thyroid tumors.