Population-based study to re-evaluate optimal lymph node yield in colonic cancer.

BACKGROUND: It is well established that lymph node (LN) yield in colonic cancer resection has prognostic significance, although optimal numbers are not clear. Here, LN thresholds associated with both LN positivity and survival were evaluated in a single population-based data set. METHODS: Treatment records were linked to the Ontario Cancer Registry to identify a 25 per cent random sample of all patients with stage II/III colonic cancer between 2002 and 2008. Multivariable regression and Cox models evaluated factors associated with LN positivity and cancer-specific survival (CSS) respectively. Optimal thresholds were obtained using sequential regression analysis. RESULTS: On adjusted analysis of 5508 eligible patients, younger age (P < 0·001), left-sided tumours (P = 0·003), higher T category (P < 0·001) and greater LN yield (relative risk 0·89, 95 per cent c.i. 0·81 to 0·97; P = 0·007) were associated with a greater likelihood of LN positivity. Regression analyses with multiple thresholds suggested no substantial increase in LN positivity beyond 12-14 LNs. Cox analysis of stage II disease showed that lower LN yield was associated with a significant increase in the risk of death from cancer (CSS hazard ratio range 1·55-1·74; P < 0·001) compared with a greater LN yield, with no significant survival benefit beyond a yield of 20 LNs. Similarly, for stage III disease, a lower LN yield was associated with an increase in the risk of death from cancer (CSS hazard ratio range 1·49-2·20; P < 0·001) versus a large LN yield. In stage III disease, there was no observed LN threshold for survival benefit in the data set. CONCLUSION: There is incongruity in the optimal LN evaluation for colonic cancer. Although the historically stated threshold of 12 LNs may ensure accurate staging in colonic cancer, thresholds for optimal survival are associated with far greater yields.