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Regional lymph node involvement in lung cancer is heterogeneous. From micrometastases in intrapulmonary lymph nodes—coded as N1(mi)—to bulky contralateral nodal disease—coded as N3—the different situations in between vary in anatomic extent and prognosis. However, regardless of the amount of tumour burden in the regional lymph nodes, the present nodal staging of the tumour, node and metastases (TNM) classification of lung cancer defines the extent of nodal involvement solely via anatomic location.1
Several studies have found that within every N category, there are prognostic modifiers. Thus, for pathologically staged I tumours, the number of removed lymph nodes at thoracotomy seems to have prognostic impact, although the cut-off varies in different studies from six to more than 15 removed lymph nodes.2 3 Within the N1 category, involvement of hilar (main bronchi) lymph nodes has been consistently associated with worse prognosis compared with involvement of intrapulmonary lymph nodes.4 5 Other indicators of worse prognosis in N1 disease are macroscopic nodal involvement and multiple nodal involvement,6 involvement of multiple nodal stations,7 and metastatic involvement—as opposed to direct nodal invasion, at least, in squamous cell carcinomas.8 As for N2 disease, skip pathologic (p) N2 (ie, pN2 without pN1 disease) is associated with better prognosis than pN2 with pN1.9 Single nodal station pN2 also has better prognosis than multiple nodal station pN2.10 Clinically evident multilevel N2 disease and bulky disease also have an adverse effect on prognosis, as well as the involvement of the highest mediastinal lymph node and extranodal extension. Even the specific nodal involvement depending on the lobar location of the primary tumour seems to have prognostic impact: superior mediastinal and aortic nodal disease with right and left upper lobe tumours, respectively, seem to have a better prognosis than the involvement of lower mediastinal nodes with …
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