The most sensitive neuroendocrine biomarker is NCAM/CD56 (expressed in 92–98% of cases) but it has low specificity since it is also expressed in 10% of lung adenocarcinomas (LUADs), lung squamous cell carcinomas (LSCCs) and non-neuroendocrine large-cell carcinomas. This evidence concerns the gene NCAM1 and lung adenocarcinoma.