Cytological characteristics of pulmonary large cell neuroendocrine carcinoma

To establish cytological features of pulmonary large cell neuroendocrine carcinoma (LCNEC), we evaluated the cytological characteristics of LCNEC. Samples from 25 histologically confirmed LCNECs (14 touch imprint (TI) and 11 curettage) were analyzed. The findings were compared with those for seven small cell lung carcinomas. Cytological findings of TIs were as follows: Tumor cells were medium- to large-sized, round or polygonal, and nuclear polymorphism was observed. Some of the tumor cells had clearly identified cytoplasms, but naked nuclei were frequently observed. Nuclei were round, oval, or polygonal, and possessed thin and smooth nuclear membranes. The nuclear chromatin pattern was finely or coarsely granular. One or two nucleoli were observed in the nuclei, but were inconspicuous in some cases. Tumor cells appeared in clusters, and rosette formation was observed, but single cells were frequently observed also. Necrotic background and nuclear streaking were frequently observed. In brush or curettage specimens, the number of cells observed on a glass was small, but the findings were almost the same as those for the TI samples. TI samples have characteristic features, such as a neuroendocrine morphologic pattern, large cell size, abundant cytoplasm, finely or coarsely granular chromatin of the nucleus, and prominent nucleoli, and the diagnosis of LCNEC is possible. In brush or curettage specimen, the LCNEC diagnosis may be possible if a sufficient number of tumor cells are obtained.