Non-Lobe Specific Metastases in Occult N2 after Lobectomy for Clinical N0 Non-Small Cell Lung Cancer

Objectives: Non-small cell lung cancer can spread into lobe specific stations and non-lobe-specific mediastinal lymph nodes. We evaluated frequency and features of non-lobe specific nodal metastases, focusing especially on the prognostic value of only non-lobe specific N2-metastases after lobectomy. Methods: We performed a retrospective review of 550 patients with non-small cell lung cancer with clinical N0, undergoing lobectomy and systematic or lobe specific node dissection. We evaluated disease free and overall survival rates using Kaplan-Meier method and significance was tested by log-rank test. Result: Occult N2 disease was detected in 68 patients (8.1%), 26 of them (38.2%) had metastases in non-lobe specific stations. Comparing patients with lobe and non-lobe specific lymph node metastases, 3-years DFS rate was 44.4% vs. 20.0% (p-value = 0.009), while 3-years OS rate was 87.3% vs. 26.7% (p-value <0.001). Among patients with non-lobe specific metastases 16 of them (61.5%) had only non-lobe specific metastases, the remaining 10 patients (38.5%) had metastatic lymph node at the same time in non-lobe specific station but also in lobe-specific stations. Comparing post-operative survival between patients with only non-lobe specific metastases and synchronous lobe and non-lobe specific metastases, 3-years DFS rate was 12.5% vs. 41.3% respectively (p-value = 0.03), and 3-years OS rate was 12.5% vs 76.7% (p-value = 0.002). Conclusion: In patients with occult N2 disease, the finding of a metastatic lymph node in a non-lobe specific station relates with significant lower survival rate. The subset of patients who presented only non-lobe specific node metastases showed a significant lower survival rate compared to the remaining occult N2.