The significance of microscopically positive lymph node margins (R1) following surgical resection for stage III colon cancer:A retrospective, observational study

Introduction:<br/>Microscopically positive resection margins (R1) are associated with poorer outcomes in colon cancer. Whilst the sequalae of a positive margin related to the primary tumour (R1Tumour) are relatively well known, comparatively less is known when the positive margin pertains to a metastatic lymph node (R1LNM). This study aims to confirm the significance and impact of R1LNM margins in colon cancer patients.<br/><br/>Methods:<br/>A retrospective, observational study of patients treated for AJCC stage 3 colon cancer treated with potentially curative surgical intervention during a 10-year study period was performed. Patients were stratified into three groups (R0, R1Tumour, R1LNM). Outcomes measured were disease specific survival (DSS), local recurrence free survival (LRFS), and systemic recurrence free survival (SRFS). Cox multivariable analysis and sensitivity analyses (time stratified, competing risk, and propensity matched analyses) were performed to determine the independent importance of R1LNM. <br/><br/>Results:<br/>A total of 801 patients were included. R1 resection rate was 6.6% and the R1LNM resection rate was 4.7%. Compared to R0 resection, R1LNM margins had significantly lower 5-year DSS (R1LNM: 53.8% [95% CI: 37.4– 77.3] vs R0: 74.2%,), LRFS (R1LNM: 61%, [95% CI: 41.7 – 89.1] vs R0: 80.5%) and SRFS (R1LNM: 39.5% [95% CI: 24.2 – 63.8] vs R0: 70%). R1LNM was not independently associated with the above outcomes following traditional, time stratified, and competing risk multivariable analyses, nor following propensity matching. <br/><br/>Conclusion:<br/>R1LNM positivity may reflect other poor prognosis variables, which themselves play a more substantial role in determining disease outcomes.<br/>