Extent of resection and lymph node evaluation in early stage metachronous second primary lung cancer: a population-based study

Background: Evidence of the optimal surgery strategy for early stage metachronous second primary lung cancer (SPLC) has been limited and controversial. This study aims to compare the survival outcomes of different extents of resection and lymph node evaluation in these patients. Methods: Early stage metachronous SPLC patients, who had received lobectomy for initial primary lung cancer (IPLC) and developed SPLC more than 3 months later, were selected from the Surveillance, Epidemiology, and End Results (SEER) database according to the American College of Chest Physicians (ACCP) guideline. Overall survival (OS) and lung cancer-specific survival (CSS) of different extents of resection and lymph node evaluation were analyzed using Kaplan-Meier method and multivariate Cox regression model. Results: Overall, 1,784 SPLC patients without nodal or distant metastasis were identified. Lobectomy was associated with significantly longer OS (HR: 0.83, 95% CI: 0.71-0.97, 5-year survival: 59.2% vs. 53.3%, P=0.02) and CSS (HR: 0.72, 95% CI: 0.60-0.88, 5-year survival: 71.5% vs. 63.2%, P=0.001) compared with sublobar resection. In addition, examined lymph node number >= 10 demonstrated longer OS (HR: 0.63, 95% CI: 0.50-0.81, 5-year survival: 66.6% vs. 53.9%, P<0.001) and CSS (HR: 0.54, 95% CI: 0.40-0.74, 5-year survival: 77.4% vs. 64.7%, P<0.001) compared with an examined lymph node number <10. The survival benefits of lobectomy and examined lymph node number >= 10 were further validated in multivariate Cox regression and subgroup analysis stratified by tumor size. Conclusion: Lobectomy and thorough lymph node evaluation provided significantly longer survival, and thus should be considered for early stage metachronous SPLC whenever possible.