Border between N1 and N2 stations in lung carcinoma: Lessons from lymph node metastatic patterns of lower lobe tumors

Objective: Distinction of lymph node stations is one of the most crucial topics still not entirely resolved by many lung cancer surgeons. The nodes around the junction of the hilum and mediastinum are key points at issue. We examined the spread pattern of lymph node metastases, investigated the prognosis according to the level of the involved nodes, and conclusively analyzed the border between N1 and N2 stations. Methods: We reviewed the records of 604 consecutive patients who underwent complete resection for non-small cell lung carcinoma of the lower lobe. Results: There were 390 patients (64.6%) with N0 disease, 127 (21.0%) with N1, and 87 (14.4%) with N2. Whereas 11.3% of patients with right N2 disease had skip metastases limited to the subcarinal nodes, 32.6% of patients with left N2 disease had skip metastases, of which 64.2% had involvement of N2 station nodes, except the subcarinal ones. The overall 5-year survivals of patients with N0, N1, and N2 disease were 71.0%, 50.8%, and 16.7%, respectively (N0 vs N1 P = .0001, N1 vs N2, P < .0001). Although there were no significant differences in survival according to the side of the tumor among patients with N0 or N1 disease, patients with a left N2 tumor had a worse prognosis than those with a right N2 tumor (P = .0387). The overall 5-year survivals of patients with N0, intralobar N1, hilar N1, lower mediastinal N2, and upper mediastinal N2 disease were 71.0%, 60.1%, 38.8%, 24.8%, and 0%, respectively. Significant differences were observed between intralobar N1 and hilar N1 disease (P = .0489), hilar N1 and lower mediastinal N2 disease (P = .0158), and lower and upper mediastinal N2 disease (P = .0446). Also, the 5-year survivals of patients with involvement up to station 11, up to station 10, and up to station 7 were 41.4%, 37.9% and 37.7%, respectively (difference not significant). Conclusions: N1 and N2 diseases appeared as a combination of subgroups: intralobar N1 disease, hilar N1 disease, lower mediastinal N2 disease, and upper mediastinal N2 disease. Interestingly, the survivals of patients with involvement up to interlobar nodes (station 11), main bronchus nodes (station 10), and subcarinal nodes (station 7) were identical. These data constitute the basis for a larger investigation to develop a lymph node map in lung cancer.