Positive impact of the negative lymph node count on the survival rate of stage III colon cancer with pN1 and right-side disease

Background: We aimed to investigate the role of the negative lymph node count (NLN) as a predictor of prognosis in patients with stage III colon cancer. Methods: We conducted a retrospective study on patients who were diagnosed with stage III colon cancer at Sun Yat-sen University Cancer Center. According to the number of negative lymph nodes, all patients were divided into the low or high NLN group. Overall survival (OS) and disease-free survival (DFS) were assessed using the Kaplan-Meier method and log-rank test between the two groups. Univariate and multivariate Cox proportional hazards models were used to evaluate the risk factors for survival. Results: The time-dependent receiver operating characteristic (ROC) curve showed that the optimal cutoff value of NLN was nine. In total, 167 and 298 patients were distributed into the low and high NLN groups, respectively. Patients in the high NLN group tended to present with a greater proportion of right-side colon cancer and pN1 stage disease, superior DFS (P < 0.001) and OS (P = 0.001) than those in the low NLN group. Multivariable analyses confirmed increased NLN as a positive prognostic variable, independent of other potential confounding factors. Subgroup analysis showed that in patients with a right-side location, those with 9 or fewer negative lymph nodes had a 5-year OS rate of 35.4% versus 77.1% in those with more than 9 negative lymph nodes evaluated (P < 0.001). For patients with stage pN1, those with NLN exhibited an inferior 5-year OS rate than those with NLN <= 9 (71.1% vs 84.8%, respectively; P = 0.009). There was no association between the number of negative lymph nodes identified and survival for patients with stage pN2 and left-side disease. Conclusion: NLN is an important prognostic factor for stage III colon cancer patients with right-side and stage pN1 disease other than for patients with stage pN2 and left-side disease, which can be partly explained in terms of inflammation and immunity.