Histopathologic classification of small cell carcinoma of the lung: comments based on an interobserver examination.

In order to evaluate the consistency in diagnosing the morphologic subtypes of small cell carcinoma of the lung (SCCL), 93 microscopic slides were blindly classified by three panelists according to the World Health Organization's (WHO) Lung Tumor Classifications of 1967 and 1981. Unanimity in the diagnosis of SCCL as the main cell type was obtained in 91 and 94% respectively. With regard to the diagnosis of the various morphologic subtypes unanimity among the three panelists was achieved in 38% according to the WHO 1967 classification and in 54% using the 1981 classification. It is concluded that the criteria used for SCCL as a distinct histopathologic entity were reproducible among the different panelists. However, different criteria were applied in the diagnosis of the morphologic subtypes of SCCL. This fact could explain the contradictory results of clinical studies reported in the literature concerning subtyping of SCCL.