Diagnosis of LCNEC is based on the identification of neuroendocrine morphology and the expression of at least one of the neuroendocrine markers (neural cell adhesion molecule [NCAM]/CD56, chromogranin A [CgA], synaptophysin) by immunohistochemical (IHC) staining or electron microscopy (almost supplanted by IHC). This evidence concerns the gene SYP and large cell neuroendocrine carcinoma.