The number of lymph nodes evaluated for metastases during colon cancer surgery has increased markedly during the past 20 years – but the improvement is not associated with any increase in the proportion of cancers that are node-positive, according to a report in the Sept. 14 issue of JAMA.
This suggests that this "upstaging mechanism" – raising the number of lymph nodes evaluated to improve identification of lymph-node–positive cancers, and thus to tailor treatment accordingly – cannot be the primary basis for improved patient survival, said Helen M. Parsons, MPH, of the U.S. National Cancer Institute’s applied research program in Bethesda, Md., and her associates.
The investigators analyzed 20-year trends in lymph node evaluation using data from 1988-2008 from the NCI’s SEER (Surveillance, Epidemiology, and End Results) registry. They reviewed records on 86,394 adults treated with radical surgical resection of the colon for a first occurrence of invasive adenocarcinoma.
The number of lymph nodes evaluated rose markedly during the study period. In 1988-1990, only 35% of patients underwent "acceptable" lymph node evaluation, defined as examination of at least 12 lymph nodes. That rate increased to 38% in 1994-1996, to 47% in 2000-2002, and to 74% in 2006-2008, Ms. Parsons and her colleagues said (JAMA 2011;306:1089-97).
However, this increase was not associated with a rise in node-positive cancer during the same period. Patients with "very high levels of lymph node evaluation ... were only slightly more likely to have node-positive disease, compared with those with few nodes evaluated," the investigators wrote.
Meanwhile, the relative hazard of death continued to decline when more lymph nodes were evaluated whether patients had node-positive or node-negative disease. Paradoxically, the improvement was greater in node-negative than in node-positive patients.
"After adjusting for patient, tumor, and primary treatment factors, we found patients with node-negative disease had lower 5-year mortality when more lymph nodes were evaluated. This effect was unexpectedly larger than that observed for patients with node-positive disease.
"These findings suggest that providers who evaluate more lymph nodes may provide some other unmeasured care, leading to better outcomes," the researchers said.
"Alternatively, the relationship between nodes evaluated and survival may reflect an underlying interaction between the tumor and the individual, influencing survival. In other words, tumor factors may stimulate lymph nodes to enlarge, reflecting immune system recognition of the tumor and more favorable outcomes," Ms. Parsons and her associates said.
This study was limited in that SEER does not collect data pertaining to comorbidities that may have affected the surgeons’ ability to excise adequate tissue samples for lymph node evaluation, they said.
The study results suggest that some factor besides upstaging (possibly improved surgical quality or postsurgical care) "may be the driving mechanism between the lymph node–survival relationship. As a result, implementing wide-range quality improvement initiatives to increase lymph node evaluation for colon cancer may have a limited effect on improving survival in this population," they added.
No conflicts of interest were reported.