Lymph Node Ratio (LNR) Discriminates Prognostication in pN1a-b and pN2 Stage-III Colon Cancer

Background: The lymph node ratio (LNR), involved nodes/ lymph nodes examined, is associated with survival in colon cancer. Previous studies investigated the prognostic role of LNR regardless of TNM N staging or compared LNR and TNM N stages for prognostic strength. However, LNR may be utilized to obtain additional prognostic information rather than replacing TNM staging in daily practice. This study aimed to evaluate the role of LNR in TNM N stages to provide further prognostic information in daily practice. Methods: Patients with stage-III colon cancer who underwent surgery and adjuvant chemotherapy were included. pN1c tumors (tumor deposits without node involvement) and rectal cancers were excluded. Clinicopathological parameters and LNR in pN1a-b and pN2 groups were evaluated for recurrence-free survival (RFS). Results: A total of 97 patients were included [pN1a-b: n=69 (71.1%) and pN2: n=28 (28.9%)]. Median LNR in the entire population was 0.09 (0.01-0.84) with a median lymph node examined of 22 (8-89) and involved of 2 (1-17). Median RFS was not reached in the pN1a-b and pN2 groups during a median follow-up of 20.8 months (1.13-101.03), with significantly better survival of the pN1a-b group (p=0.003). Among the pN1a-b group, the LNR cut-off was set as 0.10. LNR significantly discriminated RFS (Median not-reached, p=0.001). Among the pN2 group, the LNR cut-off was set as 0.25 and LNR significantly discriminated RFS [Not reached vs. 11.40 months (95%CI: 3.57-16.83), p=0.004]. Combined pN-LNR groups revealed significant discrimination in RFS (p<0.001). RFS was not statistically different between pN2-LNR≤0.25 and pN1-LNR>0.10 groups (p=0.282). In multivariable analysis with clinicopathological parameters, only LNR was significant (p=0.023), whereas the pN stage did not remain significant (p=0.637). Conclusion: LNR adds further prognostication in pN1a-b and N2 groups. LNR may be utilized to detect patient subgroups in different TNM N sages (pN1a-b and pN2) but with similar prognoses. This further prognostic information may assist clinical decisions in practice. The results of this study emphasize an adequate and higher number of lymph node samples in surgery.