Optimal number of the examined lymph nodes for different N stages in colorectal cancer

The National Comprehensive Cancer Network (NCCN) recommends that at least 12 lymph nodes (LNs) should be harvested during radical surgery of colorectal cancer (CRC). This study aims to clarify the optimal number of LNs that should be examined during the radical surgery for CRC patients with each N stage. The SEER database (n = 48,331) served as the primary cohort, while the Xijing cohort (n = 4447) was used for external validation. A Cox proportional hazards regression model was employed to evaluate risk factors associated with overall survival (OS) in CRC. Moreover, the restricted cubic splines (RCS) method was used to detect inflection points within the risk function and to investigate the correlation between the number of examined lymph nodes (ELNs) and OS. Ultimately, the optimal number of ELNs for patients at different N stages was determined and verified. The analyses from both databases consistently indicated that a higher number of ELNs is an independent prognostic factor for the OS of patients with CRC. 18 and 19 are identified as the optimal numbers of ELNs for N0, N1a, and N1b, N2a stages, respectively. The Kaplan-Meier analysis revealed that there was a statistical difference in the OS between patients in the limited group and those in the adequate group among the neighboring N subgroups. For CRC patients with different N stages, the number of LNs that needs to be cleared varies. Number of ELNs exceeded 18, 18, 19 and 19 could significantly improve the prognosis of patients with N0, N1a, N1b and N2a stages, respectively.