Lymph Node Evaluation for Colon Cancer

Cancer care can be made more successful through accurate staging and appropriate treatment, making mechanisms for definitive diagnosis of interest to policymakers. Patients with colon cancer who are treated surgically have better survival when more lymph nodes are evaluated, according to several studies; improvements in survival have reached nearly 20% in some settings. According to researchers, the mechanism associated with the improved survival rate suggests that evaluation of more lymph nodes would reduce the risk of understaging, possibly identifying a patient with node-positive disease as node negative and failing to prescribe adequate treatment. The majority of practice organizations and consensus panels recommend the surgical evaluation of ≥12 lymph nodes when staging newly diagnosed colon cancer patients; however, recent studies have questioned the mechanism of understaging, raising the possibility that increasing the number of evaluated lymph nodes may not have a major role in improved survival. In patients ≥65 years of age, increasing the number of evaluated lymph nodes has not shown improved staging or survival rates. Other studies have not shown a clear connection between the number of nodes evaluated and improved staging and survival. Higher lymph node evaluation has not consistently led to finding higher-staged cancers in select populations, creating uncertainty about the hypothesis that minimizing understaging is the mechanism for the relationship between evaluation of lymph nodes and improved survival. To further evaluate the mechanism, researchers recently conducted an observational cohort study to analyze 20-year trends in the degree of lymph node evaluation for colon cancer and the association of those trends with survival. They reported results of the study in the Journal of the American Medical Association [2011;306(10):1089-1097]. The primary outcome measure was the relationship between lymph node evaluation and node positivity. The researchers utilized data from 1988 through 2008 from the Surveillance, Epidemiology, and End Results program to identify 86,394 patients with a diagnosis of colon cancer who were surgically treated. Inclusion criteria were >18 years of age diagnosed with first invasive adenocarcinoma of the colon from January 1, 1988, through December 31, 2008, and radical resection of the colon cancer as first course of treatment. Patients were excluded if their cancer was diagnosed by autopsy or first cited on the death certificate. Other exclusion criteria were preoperative irradiation and unknown number of nodes examined. Between the 1988-1990 and 2006-2008 study periods, the proportion of patients diagnosed at <50 years of age increased from 6% (n=715) to 9% (n=1234) (P<.001). During the same time period, the proportion of proximal tumors increased from 55% (n=6191) to 62% (n=8231) (P<.001). Patients in the study cohort with proximal tumors were diagnosed at an earlier American Joint Committee of Cancer (AJCC) stage; in 1988-1990, 16% (n=1795) of tumors were classified as AJCC stage I, compared with 25% (n=3270) in 2006-2008 (P<.001). There was a marked increase in lymph node evaluation from 1988 to 2008. In 1988-1990, 34.6% (n=3875) of patients received acceptable (≥12) lymph node evaluation; by 1994-1996, 37.9% (n=4362) of patients had ≥12 lymph nodes evaluated. The percentage of those having ≥12 lymph nodes evaluated increased to 46.8% (n=6175) in 2000-2002 and 73.6% (n=9798) in 2006-2008 (P<.001). The increase in number of lymph nodes evaluated did not result in an increase in node-positive cancers during the study period; however, there were statistically significant but clinically modest increases between T stages in the proportion of node-positive cancers as the rates of lymph node evaluation increased. Patients with T2 tumors had consistent rates of node positivity, whereas those with T3 tumors had statistically significant increases in node positivity (38.8% in 1998-1990 to 49.8% in 2006-2008; P<.001) in addition to T1 and T4 tumors. Patients with high rates of lymph node evaluation were only slightly more likely to have node-positive disease; however, they experienced a significantly lower relative hazard of 3-year death compared with those with fewer nodes evaluated (adjusted hazard ratio for 30-39 nodes vs 1-8 nodes, 0.66; 95% confidence interval, 0.62-0.71; unadjusted 5-year mortality, 35.3%). Other factors associated with lower relative hazard of death were distal cancer site and later year of diagnosis; factors associated with higher 5-year relative hazard of death were older age at diagnosis, black race, more advanced AJCC stage, and high tumor grade (P<.05). In their conclusion, the researchers stated, “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.”