Association between lymph node evaluation for colon cancer and node positivity over the past 20 years

Context: Among patients surgically treated for colon cancer, better survival has been demonstrated in those with more lymph nodes evaluated. The presumed mechanism behind this association suggests that a more extensive lymph node evaluation reduces the risk of understaging, leading to improved survival. Objective: To further evaluate the mechanism behind lymph node evaluation and survival by examining the association between more extensive lymph node evaluation, identification of lymph node-positive cancers, and hazard of death. Design: Observational cohort study. Setting: Surveillance, Epidemiology, and End Results (SEER) program data from 1988 through 2008. Patients: 86 394 patients surgically treated for colon cancer. Main Outcome Measure: We examined the relationship between lymph node evaluation and node positivity using Cochran-Armitage tests and multivariate logistic regression. The association between lymph node evaluation and hazard of death was evaluated using Cox proportional hazards modeling. Results: The number of lymph nodes evaluated increased from 1988 to 2008 but did not result in a significant overall increase in lymph node positivity. During 1988-1990, 34.6% of patients (3875/11 200) had 12 or more lymph nodes evaluated, increasing to 73.6% (9798/13 310) during 2006-2008 (P<.001); however, the proportion of nodepositive cancers did not change with time (40% in 1988-1990,42%in 2006-2008, P=.53). Although patients with high levels of lymph node evaluation were only slightly more likely to be node positive (adjusted odds ratio for 30-39 nodes vs 1-8 nodes, 1.11; 95% CI, 1.02-1.20), these patients experienced significantly lower hazard of death compared with those with fewer nodes evaluated (adjusted hazard ratio for 30-39 nodes vs 1-8 nodes, 0.66; 95% CI, 0.62-0.71; unadjusted 5-year mortality, 35.3%). Conclusion: The number of lymph nodes evaluated for colon cancer has markedly increased in the past 2 decades but was not associated with an overall shift toward higher-staged cancers, questioning the upstaging mechanism as the primary basis for improved survival in patients with more lymph nodes evaluated.