title: Clinical usefulness of the WHO histological classification of thymoma.
abstract: OBJECTIVE
  Rosai et al. published the World Health Organization (WHO) classification of thymic epithelial tumors in 1999, and its clinical usefulness seems to be established. It is our purpose to find the clinically relevant diagnostic points in the WHO Histological Classification of Thymoma.
  
  
  METHODS
  Thymomas surgically removed from 100 consecutive patients at Juntendo University Hospital between October 1983 and February 2002 were classified according to the WHO histological classification. We assessed overall survival and recurrence-free rate calculated for each tumor type in the WHO classification compared with those of tumors classified by the Masaoka system.
  
  
  RESULTS
  The thymic epithelial tumors in this series comprised 10 type A, 15 type AB, 18 type B1, 21 type B2, 33 type B3, and 3 type C tumors according to the WHO classification. Based on the Masaoka system, the disease was stage I in 53 patients, stage II in 30, stage III in 15, and stage IV in 2. The 15-year recurrence-free rate was 100% for type A, AB and B1, while the rates for types B2 and B3 were 66.7% and 54.5%, respectively. The 10-year recurrence-free rate was 66.7% for type C. The 15-year recurrence-free rate of the 64 patients with type A, AB, B1, and B2 thymomas was significantly higher from that of the 33 patients with type B3 thymoma (p=0.0026).
  
  
  CONCLUSIONS
  When using the WHO classification, it is critical to distinguish type B3 thymoma from other tumor types.
authors.affiliation: Department of General Thoracic Surgery, Juntendo University School of Medicine, Tokyo, and Department of Clinical Laboratory, Labor Welfare Corporation Kanto Rosai Hospital, Kanagawa, Japan.
authors.forename: Satoshi
authors.initials: S
authors.lastname: Sonobe
authors.forename: Hideaki
authors.initials: H
authors.lastname: Miyamoto
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Izumi
authors.forename: Bunsei
authors.initials: B
authors.lastname: Nobukawa
authors.forename: Toshiro
authors.initials: T
authors.lastname: Futagawa
authors.forename: Akio
authors.initials: A
authors.lastname: Yamazaki
authors.forename: Tumin
authors.initials: T
authors.lastname: Oh
authors.forename: Toshimasa
authors.initials: T
authors.lastname: Uekusa
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Abe
authors.forename: Koichi
authors.initials: K
authors.lastname: Suda
mesh_terms: D000328:Adult; D000368:Aged; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013945:Thymoma / Q000145:classification* / Q000401:mortality / Q000473:pathology*; D013953:Thymus Neoplasms / Q000145:classification* / Q000401:mortality / Q000473:pathology*; D014944:World Health Organization