title: Interobserver variation in the classification of thymic tumours--a multicentre study using the WHO classification system.
abstract: OBJECTIVE
  To test the reproducibility of the current World Health Organization (WHO) classification of thymic epithelial tumours and to determine the level of interobserver variation within a group of pathologists, all with experience and expertise in thoracic pathology.
  
  
  RESULTS
  Ninety-five thymic tumours were circulated to a group of 17 pathologists in the UK and The Netherlands over a 1-year period. Participants were asked to classify them according to WHO criteria. The diagnoses were subjected to statistical analysis and kappa values calculated. The overall level of agreement was moderate (kappa 0.45). When the categories were reduced in number by creating two groups, (A + AB + B1 + B2 and B3 + C), the level of agreement increased to 0.62. An alternative grouping (A + AB + B1 and B2 + B3 + C) increased it slightly further. The best agreement was in tumour types A and AB. Difficulties arose in distinguishing B1 tumours from B2 tumours and B2 tumours from B3 tumours.
  
  
  CONCLUSIONS
  Although the WHO system describes a number of well-defined tumour types with clear diagnostic criteria, the overall level of agreement was moderate and improved if some groups were amalgamated.
authors.affiliation: Department of Pathology, Leeds Teaching Hospital NHS Trust, Leeds, UK.
authors.forename: E T
authors.initials: ET
authors.lastname: Verghese
authors.forename: M A
authors.initials: MA
authors.lastname: den Bakker
authors.forename: A
authors.initials: A
authors.lastname: Campbell
authors.forename: A
authors.initials: A
authors.lastname: Hussein
authors.forename: A G
authors.initials: AG
authors.lastname: Nicholson
authors.forename: A
authors.initials: A
authors.lastname: Rice
authors.forename: B
authors.initials: B
authors.lastname: Corrin
authors.forename: D
authors.initials: D
authors.lastname: Rassl
authors.forename: G
authors.initials: G
authors.lastname: Langman
authors.forename: H
authors.initials: H
authors.lastname: Monaghan
authors.forename: J
authors.initials: J
authors.lastname: Gosney
authors.forename: J
authors.initials: J
authors.lastname: Seet
authors.forename: K
authors.initials: K
authors.lastname: Kerr
authors.forename: S K
authors.initials: SK
authors.lastname: Suvarna
authors.forename: M
authors.initials: M
authors.lastname: Burke
authors.forename: P
authors.initials: P
authors.lastname: Bishop
authors.forename: S
authors.initials: S
authors.lastname: Pomplun
authors.forename: S
authors.initials: S
authors.lastname: Willemsen
authors.forename: B
authors.initials: B
authors.lastname: Addis