['Neuroendocrine differentiation can be identified in 10-30% of patients with nonsmall cell lung carcinoma (NSCLC) by immunohistochemical or electron microscopic techniques. However, its clinical significance is not well established.', 'Tumors from 107 patients with Stage IIIA, IIIB, and IV NSCLC treated with cisplatin/etoposide with or without hydrazine in the North Central Cancer Treatment Group and Mayo Clinic protocols were analyzed immunohistochemically with antibodies to chromogranin A (CGA), Leu 7 (CD 57), and synaptophysin (SY). These results were compared with clinical outcomes.', 'Keratin AE1/AE3, used as a control, was positive in 99.1% of cases; 34.6% had positive staining for at least 1 neuroendocrine marker, and 11.3% had positive staining for 2 or more markers. CGA was positive in 4.7%, Leu 7 in 18.7%, and SY in 24.3% of cases. A significant increase in survival was seen in patients with tumors expressing any one neuroendocrine marker or any combination of neuroendocrine markers (P < or = 0.01). There was no correlation between the presence of neuroendocrine differentiation and either response to chemotherapy or time to disease progression (P > 0.3), nor was there any correlation between chemotherapy response, time to progression, or survival with staining intensity or percent of cells positive per case.'] Is neuroendocrine differentiation an independent prognostic factor in chemotherapy-treated nonsmall cell lung carcinoma?