An evaluation of the relationship between lymph node number and staging in pT3 colon cancer using population-based data

Purpose: The number of lymph nodes examined has been proposed as a quality benchmark for colon cancer surgery, although it is unknown whether this strategy reduces understaging. Methods: We identified 11,044 patients who underwent surgery for colon cancer with pT3 wall penetration between 1988 and 2003 from the Surveillance, Epidemiology and End Results cancer registry. We determined the proportion of patients who were node positive for each node count. We used logistic regression to predict the odds of being node positive by node count after adjusting for confounders. We used joinpoint analysis to determine whether there was a consistent relationship between node count and the odds of being node positive. Results: The proportion of patients found to be node positive increased with node count at low counts (≤5-6 nodes), but patients with 7 nodes identified were as likely to be node positive as patients with 30 or more nodes (odds ratio = 0.97; 95% CI = 0.90 -1.05). Joinpoint analysis demonstrated a dramatic increase in odds of node positivity with increasing node count to 5 nodes (slope = 0.2; P < .0001). Between 6 and 13 nodes there was a marginal increase in odds of positive nodes (slope = 0.03; P = .006), but when more nodes were evaluated, odds of node positivity actually declined (slope= -0.01; P = .04). Conclusions: Staging of pT3 colon cancer improves with increasing node count, but only when the node count is low (<5-7 nodes). At higher counts, an increased node count has marginal effects on staging.