Prognostic significance of lymph node dissection for lung cancer surgery: a narrative review

Background and Objective: Theoretically, systematic lymph node dissection (SLND) in lung cancer surgery is a technique that leaves less cancer cells behind and is speculated to improve the prognosis, but its prognostic significance still remains controversial. In addition, the social environment surrounding lymph node dissection has changed with the advent of limited surgery for peripheral small-sized lung cancer and emergence of immune check inhibitor (ICI). Therefore, we reconsidered the role of lymph node dissection. Methods: By referring to past reports, we reviewed the process leading up to the establishment of SLND in lung cancer surgery. We compared five randomized prospective comparative studies on SLND and lymph node sampling (LNS) in lung cancer surgery. Key Content and Findings: Of the five randomized prospective comparative studies, two reported an improvement in overall survival (OS) with SLND, but the remaining three reported no significant difference in OS between SLND and LNS. One out of the five reports revealed a significant increase in complications with SLND. For peripheral non-small cell lung cancer (NSCLC) cases with tumor diameter <= 2 cm and consolidation-to-tumor ratio >0.5 segmentectomy was found to significantly improve the hazard ratio of OS, when compared to a lobectomy. However, the proportion of SLND and lobe-specific lymph node dissection (L-SLND) in each group seems to be unclear. In segmentectomy, the dissection of intersegmental lymph nodes tends to be lenient, and therefore it seems necessary to examine the significance of lymph node dissection in segmentectomy. ICIs are already showing excellent effects, and it may be necessary to examine how they will be affected by removal of regional lymph nodes where cancer-specific cytotoxic T lymphocytes (CTLs) are concentrated. SLND is essential for accurate staging, but ideally-in a host with no cancer cells in the lymph node or a host with cancer cells having a high sensitivity to ICI-it might be better to leave the regional lymph node. Conclusions: SLND may not be the right choice in all cases. A time may come when the extent of lymph node dissection is determined individually for each case. Future verification results are awaited.