Reproducibility of tumour typing of lung carcinomas performed according to WHO's recommendation.

Tumour sections from 139 patients with bronchial carcinoma were classified blindly by a panel of three pathologists according to the WHO recommendation of 1981. Only sections from resected specimens were included. There was agreement among all reviewers with regard to the main WHO tumour type of 71% of the specimens. For the remainder, two reviewers agreed upon 19% whereas the tumour classification differed substantially in 10% of all cases. About half of the original diagnoses were maintained when the latter group was re-evaluated blindly. Best agreement in the whole material was noted for squamous cell carcinoma. The main difficulty was differentiation between adenocarcinoma and squamous cell carcinoma with a high malignancy grading score. Despite the improvements of the WHO classification system, our group of diagnostic problem cases was not reduced when compared with earlier classification studies.