Prognostic value of poorly differentiated carcinoma in Japanese Society of Thyroid Surgery in a series of papillary thyroid carcinoma patients: comparison with risk classification system in Kuma Hospital.

Papillary thyroid carcinoma (PTC) often has poorly differentiated components, and it is discriminated from others and classified as an independent entity in the General Rules for the Description of Thyroid Cancer by Japanese Society of Thyroid Surgery (JSTS). In this study, we compared the prognostic significance between this type of poorly differentiated carcinoma (PDC-JSTS) and our risk classification system based on pre- and intraoperative findings in a series of PTC patients. The 10-year lymph node- and distant organ recurrence-free survival (LN-DFS and DRFS) and cause-specific survival (CSS) of high-risk patients were much poorer than in PDC-JSTS patients. In multivariate analysis, PDC-JSTS independently predicted a poor prognosis, but prognostic impacts for LN-DFS, DRFS, and CSS of high-risk in our risk classification were stronger than those of PDC-JSTS. In conclusion, it is appropriate that PDC-JSTS is defined as a subtype of PTC rather than as an independent entity.