Survival difference between patients with single versus multiple metastatic lymph nodes and the role of histology in pathological stage II-N1 non-small cell lung cancer

Background: Previous studies investigating whether metastatic lymph node count is a relevant prognostic factor in pathological N1 non-small cell lung cancer (NSCLC), showed conflicting results. Hypothesizing that outcome may also be related to histological features, we determined the prognostic impact of single versus multiple metastatic lymph nodes in different histological subtypes for patients with stage II-N1 NSCLC. Methods: We performed a retrospective cohort study using data from the Netherlands Cancer Registry, including patients treated with a surgical resection for stage II-N1 NSCLC (TNM 7th edition) in 2010–2016. Overall survival (OS) was assessed for patients with single (pN1a) and multiple (pN1b) metastatic nodes. Using multivariable analysis, we compared OS between pN1a and pN1b in different histological subtypes. Results: After complete resection of histologically proven stage II-N1 NSCLC, 1309 patients were analyzed, comprising 871 patients with pN1a and 438 with pN1b. The median number of pathologically examined nodes (N1 + N2) was 9 (interquartile range 6–13). Five-year OS was 53% for pN1a versus 51% for pN1b. In multivariable analysis, OS was significantly different between pN1a and pN1b (HR 1.19, 95% CI 1.01–1.40). When stratifying for histology, the prognostic impact of pN1a/b was only observed in adenocarcinoma patients (HR 1.44, 95% CI 1.15–1.81). Conclusion: Among patients with stage II-N1 adenocarcinoma, the presence of multiple metastatic nodes had a significant impact on survival, which was not observed for other histological subtypes. If further refinement as to lymph node count will be considered for incorporation into a new staging system, evaluation of the role of histology is recommended.