Currently, no tumor marker can clearly differentiate pulmonary carcinoids. However, as a type of neuroendocrine tumor, the tumor marker used for small-cell lung cancer may be measured. Plasma ProGRP levels in patients with pulmonary carcinoids are significantly lower than those in patients with small-cell lung cancer or mixed small-cell and non-small-cell lung cancer [5]. The gene discussed is GRP; the disease is neuroendocrine neoplasm.