Original researchThe prognostic value of the number of lymph nodes removed in patients with node-negative colorectal cancer

•We compared the CSS of N0 patients with 1-7, 8-11 and ≥12 lymph node(s) removed.•We compared the CSS of N1 patients and N0 patients who had fewer lymph nodes removed.•The prognosis of N0 patients <12 lymph node(s) removed and N1 patients was similar.

Background: To investigate the prognostic significance of the number of lymph nodes removed in colorectal cancer (CRC) patients with no metastatic lymph node. Patients and methods: The clinicopathological data of 461 CRC patients was analyzed. In order to compare the survival of patients who had fewer lymph nodes removed versus the survival of patients who had 1-3 metastatic lymph node(s), a separate group of 74 N1 disease patients were also included in the study. All patient data were collected prospectively. Kaplan-Meier method was used for calculation and plotting of the survival curves of the patient groups, and log-rank test was used for the comparison of the survival curves. Results: Cancer-specific survival (CSS) rates of patients who had 1-7 lymph node(s) and 8-11 lymph nodes removed were significantly worse than those who had 12 or more lymph nodes removed (p = 0.006 and p = 0.037, respectively), while CSS was not significantly different between those who had 1-7 versus 8-11 lymph node(s) removed (p = 0.647); this grouping had independent prognostic significance in Cox analysis (p = 0.006). CSS of patients with N1 disease was not significantly different from those who had 1-7 and 8-11 lymph node(s) removed (p = 0.312 and p = 0.165, respectively), while it was significantly worse than CSS of patients who had 12 or more lymph nodes removed (p = 0.001). Conclusion: In colorectal cancer patients whose removed lymph nodes are non-metastatic, removal of at least 12 lymph nodes will determine the lymph node status reliably.