MALIGNANT MESOTHELIOMA OF THE PLEURA - INTEROBSERVER VARIABILITY

Aims-To assess the consistency of histopathological diagnosis of pleur al malignant mesothelioma by estimating interobserver agreement betwee n five pathologists. Methods-Eighty eight histological sets pertaining to original diagnoses of pleural malignant mesothelioma were reviewed separately by each pathologist. Diagnostic likelihood was graded as d efinite (A), probable (B), possible (C), improbable (D), and definitel y not (E) malignant mesothelioma. The following indexes were estimated : observed proportion of agreement (Po), kappa statistics and proporti on of agreement for ''positive'' (Ppos) and ''negative'' (Pneg) diagno ses. Results-Sixty cases (68.2%) were rated by at least three reviewer s as A or E and by none of the others as D or E. Five (5.7%) were rate d by at least two reviewers as D or E and by none of the others as A o r E. Nine (10.2%) showed a serious disagreement, rated A or B and D or E. Agreement for sets obtained at necropsy/surgery (median kappa w=0. 57) was similar to that for endoscopic material (median kappa w=0.54). Agreement was poor on material obtained by needle biopsy (median kapp a w=0.21). The median value of Ppos varied between 0.94 (necropsy/surg ery) and 0.67 (needle biopsy) and that of Pneg between 0.78 (necropsy/ surgery) and 0.34 (unspecified biopsy). Interobserver agreement on his tological typing was good overall (median kappa=0.59). Conclusions-Of the original histological diagnoses, 70% were consistently reproduced through panel review. Most indexes of agreement between pathologists r anged from poor (needle biopsy) to moderate (necropsy/surgery). Agreem ent in confirming malignant mesothelioma was greater than that regardi ng exclusion of this diagnosis. Of the cases finally considered to hav e malignant mesothelioma, the reproducibility of histological typing w as relatively satisfactory.