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Classification of follicular cell tumors of the thyroid gland: Analysis involving Japanese patients from one institute


  • Dr Kanji Kuma, the president of Kuma Hospital, passed away on 29 November 2008, during preparation of this manuscript, and all authors wish to express their deep appreciation for his helpful advice and encouragement in conducting thyroid research. Yanhua Bai received a fellowship from the Rotary Yoneyama foundation, Japan.

Kennichi Kakudo, MD, PhD, Department of Human Pathology, Wakayama Medical University, Kimiidera 811-1, Wakayama city, 641-8509 Japan. Email:


Prognostic analyses of thyroid carcinomas of follicular cell origin were carried out on patients treated at Kuma Hospital, Kobe, Japan. A new histopathological classification based on the prognostic evidence is proposed in this study, and it is applicable to the patients treated curatively. Major histological types of papillary carcinoma, follicular carcinoma and poorly differentiated carcinoma were combined into one single entity of follicular cell adenocarcinoma because (i) they have the same cell origin (follicular cell); (ii) clear-cut separation of papillary and follicular carcinoma is not always possible, and 10 year cause-specific survival was essentially similar when the patients were treated curatively; and (iii) poorly differentiated carcinoma usually has a background of either papillary or follicular carcinoma. This adenocarcinoma together with undifferentiated carcinoma was stratified into four prognostic groups using pure morphological criteria of the degree of cellular differentiation and histological grade. They are termed well-differentiated adenocarcinoma, moderately differentiated adenocarcinoma, poorly differentiated carcinoma and undifferentiated carcinoma of the thyroid. The 10 year disease-free survival rates were 86.3–93.1%, 65.4–78.7%, and 43.0–53.8%, and 0%, respectively. The 10 year cause-specific survival rates were 97.2–100%, 91.5–97.4%, and 71.2–80.0%, and 0%, respectively.