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

Aim: Microscopically positive resection margins (R1) are associated with poorer outcomes in colon cancer. While 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). The aim of this study is to confirm the significance and impact of R1LNM margins in colon cancer patients.

Method: A retrospective, observational study of patients treated for American Joint Committee on Cancer Stage 3 colon cancer 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.

Results: A total of 801 patients were included. The R1 resection rate was 6.6% and the R1LNM resection rate was 4.7%. Compared with 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.

Conclusion: R1LNM positivity may reflect other poor-prognosis variables, which themselves play a more substantial role in determining disease outcomes.