| Background Surgical resection is still the most importantmethod for the patients with non-small-cell lung cancer (NSCLC). The survival after surgical resection of patients with NSCLC is mainly determined by postoperative clinical-pathologic stage, but It is very difficult for us to understand that the tumor recurrence is not rare in stage I NSCLC. Only about 60~70% of patients with stage I NSCLC (lymph node negative ) survive by 5 years. This suggests that the clinical-pathologic staging of some patients with early stage NSCLC determined by conventional hematoxylin eosin (H&E) staining may be underestimated. Which means the presence of occult micrometastases in lymph nodes is not detected by use of H&E staining. An accurate assessment of the presence or absence of tumor cells in the regional lymph nodes is therefore critical for making accurate pathologic stage, prognosis and rational adjuvant-therapy for patients with NSCLC.With the development of modern immunology and molecular biologic techniques , detection of occult micrometasteses is becoming possible by use of immunohisto-chemical (IHC) staining analysis and reverse transciptase-polymerase chain reaction (RT-PCR). Recently along with the outcome of these new techniques, the individual orclustered tumor cells previously undetectable with H&E staining have been easily detected with an IHC staining or RT-PCR techniques within the lymph node, bone marrow or peripheral blood in many cases of breast cancer, colorectal or gastric cancer, but only a few reports about NSCLC.Methods In order to study the clinical possibility of detectingthe micrometasteses in regional lymph nodes of NSCLC, from April 2003 to February 2004, we studied the lymph node samples taken from the patients with NSCLC during the operations. Each lymph node sample was divided into two parts in equal size. At random, the one half part of the lymph node was examined with H&E staining and (or) IHC staining analysis, and the other half part of the lymph node was used for RT-PCR.We examined every lymph node sample with conventional H&E staining. Firstly, each resulting tissue block was processed for routine paraffin embedding. Then we chose 6-10 serial sections, each of 5 um thick, from every paraffin block of the lymph node. Finally, the first and the second last sections of each lymph node were stained by H&E for histologic confirmation of absence of metastatic tumor, and the other serial sections were used for the IHC staining examination with the mouse antihuman monoclonal antibody against cyokeratin (CK).All the remaining lymph node samples of each patient were mixed together for RT-PCR if they located in the same region. As long as the presence of metastatic tumor in one lymph node was found by H&Estaining, all other lymph node samples in the same region were no longer detected by IHC staining or RT-PCR techniques.Results 1. The paraffin embedded sections of 195 regionallymph nodes from 25 patients with NSCLC were examined by H&E staining. 30 lymph nodes (15.4%, 30/195) in 9 patients (36.0%, 9/25) revealed overt nodal metastases larger than 2mm in diameter, and none in 25 patients showed micrometastatic tumor cells. 2. Tissue sections from 135 regional lymph nodes of 25 patients with NSCLC that were staged as free of metastases by H&E staining were screened for micrometastases by IHC staining analysis with the mouse antihuman monoclonal antibody against cyokeratin . 31 lymph nodes (22.9%, 31/135) in 9 patients (36%, 9/25) showed single cell or cells clusters of 2mm size or smaller within the marginal sinuses or the interstitium of lymph nodes with positive CK staining. There was a significant difference between the results of H&E staining and IHC staining (P<0.05). Five of sixteen patients (31.2%, 5/16) staged as PN0had hilum lymph node micrometastases, versus four of nine patients (44.4%, 4/9) with stage PNi had mediastinal lymph node micrometastases (P<0.05, significant difference between two groups). The IHC staining confirmed that there was no overt nodal met...
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