Reproducibility of the WHO/IASLC grading system for pre-invasive squamous lesions of the bronchus: a study of inter-observer and intra-observer variation

Aims: Although many workers have graded preinvasive squamous lesions arisin g in the bronchus, there has been no consensus classification system until the latest edition of the WHO/IASLC histological classification of pulmonar y and pleural tumours. Because the value of any such system is dependent on its reproducibility, we have circulated a series of such lesions to a pane l of histopathologists to assess interobserver and intra-observer variation when the WHO/ IASLC classification was applied. Methods and results: Colour transparencies of 28 preinvasive squamous lesio ns were assessed by six histopathologists (two with a special interest in p ulmonary pathology, two generalists and two trainees) on three separate occ asions over a period of 3 months, using the criteria of the WHO/IASLC (mild , moderate and severe dysplasia, and in-situ carcinoma). An additional cate gory of metaplasia was added for those cases that showed no dysplasia. Weig hted kappa coefficents of agreement (K-w) were used to evaluate paired obse rvations with a standard quadratic weighting being employed, such that kapp a coefficients corresponded to intra-class correlation coefficients. Wilcox on's sign-ranked test was used to measure the statistical significance of g roup trends, when comparing kappa values for the three grading systems. Var ious 3-point systems were also assessed, through combination of the above g roups. Intraobserver agreement was substantially better than interobserver variation (mean: 0.71 vs, 0.55). Between the various pathologist groups, in ter-observer variation was relatively minor, although intra-observer variat ion was higher within the trainee pathologist group. Using weighted kappa v alues, there was no significant difference in either inter-observer or intr a-observer agreement between the Five point grading system and a 3-point sy stem of metaplasia/mild, moderate and severe/in-situ grades. However, there was a significant increase in variation when a 3-point system of metaplasi a/mild, moderate/severe and in-situ carcinoma was used. Conclusion: This study shows levels of interobserver and intra-observer var iation similar to those found in other grading systems in histopathology, w ith no significant decrease in variability found by abridging the system. T he WHO/IASLC system is therefore recommended for future use in both clinica l and research fields.