Objective:To explore whether the conventional pathologic stages of some non-small cell lung cancer (NSCLC) patients were underestimated.Methods:195 lymph node samples were taken from 25 NSCLC patients during the operations.Firstly,each resulting tissue block was processed for routine paraffin embedding.Then the 6～10 serial sections were chosen,each 5 μm thick,from every paraffin block of the lymph node.Finally,the first and the second last sections of each lymph node were stained by hematoxylin eosin (HE),and the other serial sections were used for the immunohistochemical (IHC) staining examination with the monoclonal antibody against cyokeratin 19.Results:With HE staining,30 of the 195 regional lymph nodes revealed dominant nodal metastases,and none showed micrometastases.IHC staining was performed on 135 lymph nodes that were identified as free of metastases by HE staining,31 showed micrometastases;none showed gross nodal metastases.There was a significant difference between HE staining staging and IHC staining staging (P<0.05).Conclusion:Conventional HE staining can accurately detect gross nodal metastases in the lymph nodes of NSCLC patients,but is unfit for detecting lymph nodal micrometastases.IHC staining analysis can significantly facilitate the detection of occult micrometastatic tumor cells in lymph nodes,and its assessment of nodal micrometastases can provide a refinement of TNM stage for NSCLC patients.Our results provide a rationale for extensive lymph nodes sampling. Objective: To explore whether the conventional pathologic stages of some non-small cell lung cancer (NSCLC) patients were underestimated. Methods: 195 lymph node samples were taken from 25 NSCLC patients during the operations. Firstly, each resulting tissue block was processed for routine paraffin embedding. from the 6 to 10 serial sections were chosen, each 5 μm thick, from every paraffin block of the lymph node. Finaally, the first and the second last sections of each lymph node were stained by hematoxylin eosin (HE), and the other serial sections were used for the immunohistochemical (IHC) staining examination with the monoclonal antibody against cyokeratin 19. Results: With HE staining, 30 of the 195 regional lymph nodes revealed dominant nodal metastases, and none showed amplified signals 135 lymph nodes that were identified as free of metastases by HE staining, 31 showed micrometastases; none showed gross nodal metastases. There was a significant difference between HE st Confocal: Conventional HE staining can accurately detect gross nodal metastases in the lymph nodes of NSCLC patients, but is unfit for detecting lymph nodal micrometastases. IHC staining analysis can significantly facilitate the detection of occult micrometastatic tumor cells in lymph nodes, and its assessment of nodal micrometastases can provide a refinement of a TNM stage for NSCLC patients. Our results provide a rationale for extensive lymph node sampling.