SCLC is an aggressive neuroendocrine tumour; therefore, neuroendocrine markers such as NSE, chromogranin A (CGA) and pro-gastrin-releasing peptide (ProGRP) have been shown to be important to immunohistochemically characterize these malignant lung cancer and can be used as tumour markers released into the circulation [84]. This evidence concerns the gene ENO2 and lung carcinoma.