Comparative study for detecting micrometastases of lymph nodes in patients with lung cancer

Objective: To set up a new method to detect occult micrometastases of lymph nodes in patients with no-small-cell lung cancer (NSCLC).

Methods: We had detected 195 lymph node samples taken from 25 patients with NSCLC during the operations. Each lymph node sample was divided into two same parts in size. The one half part of lymph node should be examined by conventional histopathologic examination and immunohistochemical (IHC) staining. All the remaining lymph node samples of each patient should be mixed together for the reverse transcriptase-polymerase chain reaction (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&E staining, all other lymph node samples in the same region should not be detected by IHC staining or RT-PCR techniques.

Results: Frozen tissue sections of 135 lymph nodes that were staged as free of metastases by conventional histopathologic examination were screened by IHC staining. 31 lymph nodes showed single cell or cells clusters. Of 39 groups mixed regional lymph nodes which were diagnosed to be devoid of metastases by conventional histopathologic examination, 11 groups were found to have positive reactions to cytokeratin 19-mRNA by RT-PCR. There was a correlation between IHC staining and RT-PCR for detection of nodal micrometastases of NSCLC (U = 7.682, P = 0.0001).

Conclusions: IHC staining analysis can facilitate the detection of occult micrometastases in lymph nodes of NSCLC, and its assessment of nodal micrometastases can provide a refinement of TNM stage for partial patients with stage I to II. RT-PCR has the same value as IHC staining in detection of lymph nodal micrometastases. RT-PCR technique can reduce expense of the detecting micrometastases in lymph nodes.