Superior and Basal Segment Lung Cancers in the Lower Lobe Have Different Lymph Node Metastatic Pathways and Prognosis

Background Although the lower lobe is a large entity that occupies half of the hemithorax, all tumors located within the lower lobe have been treated uniformly regardless of tumor location. The aim of this study was to reveal differences in the metastatic pathway to the mediastinum and in prognosis of N2 disease between lung cancers originating from superior and basal segment of the lower lobe. Methods Data on 139 patients who underwent pulmonary resection with systematic nodal dissection for pN2 non-small cell lung cancer (NSCLC) originating from the lower lobe between 1980 and 2001 were retrospectively reviewed. Those lower lobe N2 tumors were divided into two groups by origin: 51 were superior segment, and 88 were basal segment. Results The superior segment group showed a significantly higher incidence of superior mediastinal metastasis than the basal segment group (64% vs 36%, p = 0.0012). When superior mediastinal metastasis existed, the basal segment group showed a significantly higher incidence of synchronous subcarinal metastasis than the superior segment group (81% vs 39%, p = 0.0006). Pneumonectomy was required significantly more often in the superior segment group than in the basal segment group (45% vs 17%, p = 0.0003). The basal segment origin tumors with only subcarinal metastasis showed significantly better prognosis than other lower lobe N2 tumors (5-year survival, 43% vs 18%; p = 0.0155). Conclusions Basal segment tumor metastasizes to the superior mediastinum mostly through the subcarinal node, whereas superior segment tumors often metastasize directly to the superior mediastinum without concomitant metastasis to the subcarinal node. Superior mediastinal dissection will be mandatory for accurate staging of superior segment tumors even when the subcarinal node is negative on frozen section. As for the prognosis among lower lobe N2 tumors, only in cases with basal segment tumor without superior mediastinal metastasis may long-term survival be expected.