Mode of spread in the early phase of lymphatic metastasis in non-small-cell lung cancer: significance of nodal micrometastasis.

The impact of lymphatic micrometastases on prognosis of non-small-cell lung cancer has not been clearly established. We therefore prospectively assessed the frequency, mode of mediastinal spread, and prognostic significance of lymphatic micrometastases in lymph nodes of 93 patients with completely resected non-small-cell lung cancer staged as pT1 to pT4 pN0 and pN1 by conventional histopathologic techniques. Frozen tissue sections from 471 lymph nodes that were staged as free of metastases by routine histopathologic examination were screened for micrometastases by the alkaline phosphatase-antialkaline phosphatase immunostaining technique with the monoclonal antibody Ber-Ep-4. Twenty of 73 patients (27.4%) with disease staged as pN0 and nine of 20 patients (45.0%) with disease staged as pN1 had nodal micrometastases. Eight of 17 patients with upper lobe primary tumors and five of 12 patients with lower lobe primary tumors exhibited skip micrometastases. Mean relapse-free survival was significantly increased in patients with pN0 disease without micrometastases (41.1 vs 29 months, p = 0.0081). In patients with pN1 disease, mean relapse-free and cancer-related survivals were also significantly increased if no micrometastases were found (34.8 and 38.2 months vs 18 and 23.5 months, p = 0.0157 and p = 0.0094). Patients with disease staged as pN0 and pN1 with micrometastases revealed no difference in cancer-related survival compared with a control population of patients with disease staged as pN2. The mode of spread was erratic. The prognosis of patients after upstaging of pN0 and pN1 disease according to results of immunohistochemical staining correlated strongly with the prognosis of patients whose disease was staged at the higher stages by conventional histopathologic examination. These findings could represent a new indication for adjuvant therapy, supporting extensive lymph node sampling for staging purposes.