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

Department of Pathology, Leeds Teaching Hospital NHS Trust, Leeds, UK.
Histopathology (Impact Factor: 3.45). 09/2008; 53(2):218-23. DOI: 10.1111/j.1365-2559.2008.03088.x
Source: PubMed


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.
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.
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.

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    • "Thymomas comprise a spectrum of unique thymic epithelial tumors that generally show intratumoral thymopoiesis. They are subdivided into WHO type A, AB, B1, B2, and B3 thymomas (1, 2), but this classification has been challenged by some authors (3, 4). Thymic carcinoma also show a spectrum subtypes that resemble analogously called extrathymic carcinomas (TCs) (2, 5). "
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    • "To this day pathologists everywhere in the world rely upon haematoxylin and eosin (H&E) labelled tissue sections to diagnose cancer using a compound light microscope. Diagnostic criteria and current classification systems in clinical use for human cancers remain largely morphology based [3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26], with their attendant problems with interobserver variability [27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45]. Notable exceptions are the classification systems of neoplasms of haematopoietic and lymphopoietic systems, which are now heavily reliant upon ancillary technologies [46]. "
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    • "Thus, from type A to type C, there is a clear deterioration of prognosis; A, AB, B1 and B2 show a progressively worse outcome; B3 (the old 'well-differentiated thymic carcinoma') is more aggressive and shows intermediate survival, while patients with type C lesions present the worse outcome, with poor survival and high recurrence rate. Although the WHO system describes a number of welldefined tumour types with clear diagnostic criteria, the overall level of agreement is moderate with recognised intraand inter-observer discrepancies [64]; however, it could be improved if some groups are amalgamated. A meta-analysis "
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