Lymph Node Harvest in Colon Cancer: Influence of Microsatellite Instability and Proximal Tumor Location

Background At least 12 harvested lymph nodes are recommended for proper staging of colon cancer. The effect of tumor-related factors associated with lymph node harvest is not well understood as data are lacking. We investigated tumor-related factors in relation to the number of lymph nodes harvested. Methods Patient and tumor characteristics were investigated in relation to harvested lymph nodes (LN >= 12), number of metastatic nodes, LN ratio (LNR), and prognosis with univariate and multivariate analyses. Results An LN harvest >= 12 nodes was achieved in 36% of the patients. Having <12 nodes harvested was not associated with increased risk for locoregional recurrence, distant metastasis, or decreased survival. Tumor size >5 cm, microsatellite instability (MSI), and proximal tumor location predicted a harvest of LN >= 12. The highest rate (54%) of LN >= 12 was found for MSI cancers [ odds ratio (OR) 2.9, 95% confidence interval (CI) 1.3-6.5; P = 0.011]. Multivariate analysis identified a proximal location as an independent factor of LN >= 12 (adjusted OR 3.5, 95% CI 1.5-8.2; P = 0.003), with MSI an independent factor in stage II to III colon cancer (adjusted OR 2.6, 95% CI 1.1-6.0; P = 0.026). To determine the best prognosticator, LNR was the only significant factor in the multivariate analysis (Cox proportional hazards) with a hazard ratio (HR) of 2.9 (95% CI 1.1-7.8; P = 0.038) for LNR 0.01-0.17 and an HR of 5.8 (95% CI 2.5-13.1; P < 0.001). Conclusions Proximal tumor location and microsatellite instability are associated with a higher number of lymph nodes harvested, pointing to possible underlying genetic and immunologic mechanisms. The LNR is an independent prognostic variable for colon cancer.