Interobserver variation in the classification of thymic tumours - a multicentre study using the WHO classification system

• Published in: Histopathology Vol. 53; no. 2; pp. 218 - 223
• Main Authors: Verghese, E T, Den Bakker, M A, Campbell, A, Hussein, A, Nicholson, A G, Rice, A, Corrin, B, Rassl, D, Langman, G, Monaghan, H, Gosney, J, Seet, J, Kerr, K, Suvarna, S K, Burke, M, Bishop, P, Pomplun, S, Willemsen, S, Addis, B
• Format: Journal Article
• Language: English
• Published: Oxford, UK Blackwell Publishing Ltd 01-08-2008; Blackwell
• Subjects: Biological and medical sciences; Humans; interobserver agreement; Investigative techniques, diagnostic techniques (general aspects); kappa; Medical sciences; Observer Variation; Pathology. Cytology. Biochemistry. Spectrometry. Miscellaneous investigative techniques; Pneumology; Prognosis; Reproducibility of Results; Severity of Illness Index; thymic carcinoma; thymoma; Thymoma - classification; Thymoma - epidemiology; Thymoma - pathology; Thymus Neoplasms - classification; Thymus Neoplasms - diagnosis; Thymus Neoplasms - epidemiology; Thymus Neoplasms - pathology; Tumors of the respiratory system and mediastinum; WHO classification; World Health Organization; thymic carcinoma; Thymus gland; Thymoma; Mediastinum disease; Thymus carcinoma; Malignant tumor; Thymus pathology; Agreement; Anatomic pathology; Classification; interobserver agreement; Thymic epithelial tumor; kappa; Benign neoplasm; WHO classification; Cancer; WHO
• ISSN: 0309-0167; 1365-2559
• DOI: 10.1111/j.1365-2559.2008.03088.x

Aims:  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.
Methods and 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 κ values calculated. The overall level of agreement was moderate (κ 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.