[Outline of general rules for the description of thyroid cancer (6th edition)]

General rules for the description of thyroid tumors is essential for the medical practice on thyroid tumors. The Japanese Society of Thyroid Surgery has published the general rules since 1977, and has revised it 5 times according to the revision of UICC TNM classification or WHO histological classification by the latest 6th edition of the rules published in 2005. In the present revision of the rules TNM and Ex (extra thyroidal invasion) classifications were reconsidered as compared with UICC TNM classification, in which the tumor size of T1 and T2 was altered and the concept of Ex classification was reflected to T3 and T4, and the region of N1a and N1b was also altered. The histological classification was revised according to that of WHO in which the poorly differentiated carcinoma was separately classified from papillary and follicular carcinoma, and newly accepted histological types of tumor such as CASTLE and SETTLE were included. Furthermore, the handling of the resected specimens for histological examination was described precisely and the new report form of cytology was presented.