Fig. 2

Microscopic findings. A The tumor was composed of exophytic, papillary growth of multilayered epithelium. Scale bar 1 mm. B A palisading pattern of columnar cells with reverse polarity was observed in the basal layer. C The tumor cells were composed of uniformly round and polygonal cells with abundant, eosinophilic cytoplasm and monomorphic round nuclei with fine chromatin. Discontinuous flattened cells were found in the outermost layer of multilayered epithelium (arrowheads). D Focal ciliated epithelium from residual respiratory mucosa was found (arrows) while no dysplasia-carcinoma sequence was observed