To clarify the biological differences between small cell lung carcinoma (SCLC) and large cell neuroendocrine carcinoma (LCNEC), we investigated the expression of two bHLH type transcription factors, human achaete-scute homolog 1 (hASH1) and hairy/enhancer of split 1 (HES1), which positively and negatively regulate the neuroendocrine differentiation of respiratory epithelial cells, respectively. Eighty-eight formalin-fixed and paraffin-embedded pulmonary carcinomas (32 SCLC, 32 LCNEC, 14 adenocarcinomas, and 10 squamous cell carcinomas) and 14 SCLC and 1 LCNEC derived cell lines were used. hASH1 and HES1 mRNA were detected using a highly sensitive in situ hybridization method with digoxigenin-labeled cRNA probes and biotinylated tyramide. The staining results were scored from 0 to 12 by multiplying the staining intensity by the percentage of positive tumor cells. The mean staining score of hASH1 mRNA was significantly higher in SCLC than in LCNEC (p<0.01); conversely, that of HES1 mRNA was lower in SCLC than in LCNEC (p<0.01). These findings reveal that SCLC more strongly expresses the neuroendocrine phenotype, while LCNEC shows characteristics more similar to the ciliated epithelium phenotype, suggesting that the biological characteristics of these two tumors are different.
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