title: WHO histologic classification is a prognostic indicator in thymoma.
abstract: BACKGROUND
  The histologic classification of thymoma has remained a subject of controversy for many years. In 1999, the World Health Organization Consensus Committee published a histologic typing system for tumors of the thymus.
  
  
  METHODS
  We reclassified a series of 100 thymomas resected at Tokushima University Hospital and four affiliated hospitals in Japan between 1973 and 2001 according to the World Health Organization histologic classification and reported its clinicopathologic relationship and prognostic relevance.
  
  
  RESULTS
  There were 8 type A, 17 type AB, 27 type B1, 8 type B2, 12 type B3, and 28 type C thymomas. The frequency of invasion to neighboring organs increased according to tumor subtype in the order A (0%), AB (6%), B1 (19%), B2 (25%), B3 (42%), and C (89%). There was no recurrence in patients with type A, AB, or B2 thymoma. The recurrence rates of patients with B1, B3, or C thymoma were 15%, 36%, and 47%, respectively. The disease-free survival rates were 100% for types A and AB, 83% for types B1 and B2, 36% for type B3, and 28% for type C thymoma at 10 years. There were significant differences in disease-free survival between types A and AB and types B1 and B2 (p = 0.0436), and between type B3 and type C (p = 0.042). By multivariate analysis, only Masaoka clinical stage (p = 0.002) showed significant independent effects on disease-free survival. The 10-year survival rates of types A and AB, types B1 and B2, type B3, and type C thymoma were 100%, 94%, 92%, and 58%, respectively.
  
  
  CONCLUSIONS
  The current study confirmed the World Health Organization histologic classification as a good prognostic factor.
authors.affiliation: Department of Oncological and Regenerative Surgery, School of Medicine, University of Tokushima, Tokushima, Japan. kondo@clin.med.tokushima-u.ac.jp
authors.forename: Kazuya
authors.initials: K
authors.lastname: Kondo
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Yoshizawa
authors.forename: Masaru
authors.initials: M
authors.lastname: Tsuyuguchi
authors.forename: Suguru
authors.initials: S
authors.lastname: Kimura
authors.forename: Masayuki
authors.initials: M
authors.lastname: Sumitomo
authors.forename: Junji
authors.initials: J
authors.lastname: Morita
authors.forename: Takanori
authors.initials: T
authors.lastname: Miyoshi
authors.forename: Shoji
authors.initials: S
authors.lastname: Sakiyama
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Mukai
authors.forename: Yasumasa
authors.initials: Y
authors.lastname: Monden
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D018572:Disease-Free Survival; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D011379:Prognosis; D015996:Survival Rate; D013945:Thymoma / Q000145:classification* / Q000401:mortality / Q000473:pathology; D013953:Thymus Neoplasms / Q000145:classification* / Q000401:mortality / Q000473:pathology; D014944:World Health Organization