Lymph Node Count in Colon Cancer Surgery May Not Add Up to Survival


ANN ARBOR, Mich., Nov. 14 -- Examining 12 or more lymph nodes after a colectomy for colon cancer, a recommended hospital quality indicator, was not associated with five-year survival, investigators here found.
Action Points
Explain to interested patients that in this study a hospital quality indicator tied to a specific number of lymph nodes examined was not associated with the length of survival after colon cancer surgery.
In a retrospective cohort study, after adjusting for various confounding factors, there remained no statistically significant relationship between lymph node examination rates and five-year survival after surgery, Sandra L. Wong, M.D., of the University of Michigan, and colleagues, reported in the Nov. 14 issue of the Journal of the American Medical Association.
"Using lymph node counts as a hospital quality indicator is gaining momentum from stakeholders in the health care community," the investigators wrote. "Efforts by payers and professional organizations to increase node examination rates may have limited value as a public health intervention," they concluded.
In an accompanying editorial, Marko Simunovic, M.D., M.P.H., of McMaster University in Hamilton, Ontario, and Nancy N. Baxter, M.D., Ph.D., of the University of Toronto, wrote that Dr. Wong and colleagues have decisively undermined the theory of understaging as a cause of poor survival.
In view of several studies finding survival risks for understaging, the National Quality Forum endorsed a 12-node minimum as a consensus standard for hospital-based performance, the researchers wrote. The move was taken in collaboration with the American College of Surgeons and the American Society of Clinical Oncology.
The Michigan group, using the Surveillance, Epidemiology, and End Results (SEER)-Medicare linked database (1995-2005), identified 30,625 U.S. patients undergoing colectomy for nonmetastatic colon cancer.
The investigators sorted the hospitals into four evenly sized groups by the proportion of patients with 12 or more nodes examined. Late survival rates were assessed for each hospital group, adjusting for potentially confounding patient and clinician characteristics.
Hospitals in the four quartiles varied widely in the number of lymph nodes examined. Only 16% of patients had at least 12 nodes examined in the hospitals in the lowest quartile versus 61% at hospitals in the highest quartile.
Hospitals with the highest proportions of patients with examination of 12 or more lymph nodes tended to treat lower-risk patients and had substantially higher procedure volumes.
After adjusting for these and other factors, there remained no statistically significant relationship between hospital lymph node examination rates and five-year survival after surgery (adjusted hazard ratio, highest versus lowest hospital quartile, 0.95, 95% confidence interval: 0.88 to 1.03).
However, improved survival was seen at the patient level. Patients with more than 12 nodes evaluated were less likely to die of colon cancer than those with fewer than 12 nodes evaluated (adjusted hazard ratio: 0.83, 95% confidence interval, 0.78 to 0.88), findings similar to those of other studies.
These data suggest that understaging is not the mechanism underlying the relationship between increased lymph node counts and improved patient survival in colon cancer.
Although the four hospital groups varied widely in the number of lymph nodes examined, they were all equally likely to find node-positive tumors and had very similar overall unadjusted rates of adjuvant chemotherapy (26% for the highest hospital quartile, versus 25% for the lowest hospital quartile), the researchers reported.
In a post hoc analysis, the researchers found that whether a hospital had high or low efficiency (the overall ratio of positive nodes to total nodes examined greater than or less than 8%), there remained no association between node counts and survival rates, the researchers said.
This analysis also suggests a simple explanation for these null findings, the researchers said. Regardless of how many lymph nodes hospitals examined, they tended to find the same number of positive nodes. As a result, higher hospital lymph node examination rates did not result in greater detection of patients with node-positive tumors or higher rates of adjuvant chemotherapy.
Reasons why hospitals that examine more nodes failed to detect more nodal metastases included variation in the extent of resection but not in the surgeon's ability to include positive nodes with the specimen, the investigators suggested.
A second reason involves the way specimens are managed in the pathology department. Also, pathologists or their staff may vary in their skill and efficiency in identifying and dissecting positive nodes. If so, more efficient clinicians may feel they need to examine fewer nodes for adequate staging, the researchers said.
This study was limited to patients older than 65. Although stratified analysis found no significant evidence that patients' age was an important factor, the generalizability of these findings to patients younger than 65 is not known, they said.
In the accompanying editorial, Drs. Simunovic and Baxter wrote that "the most likely explanation of the findings from the
SEER is confounding; there is an unidentified factor(s) that is related to both the exposure (i.e., lymph node count) and the outcome (i.e., patient survival), leading to an apparent but spurious association between the exposure and outcome."
They indicated that "three lessons for users of quality indicators can be learned from this study."
First, quality indicators supported only by observational studies should be used with caution.
Second, they said, use of quality indicators can lead to unintended consequences. For example, the use of defatting solutions to assist in identifying nodes is not only expensive but may expose pathology personnel to toxic substances.
Third, quality indicators, including financial bonuses for improved performance, may go to those with better past performance and may not directly result in quality improvement.
"Using quality indicators as one part of a comprehensive, supportive, incremental quality improvement project, such as those included under the rubric of total quality management or continuous quality improvement, is likely to be more constructive -- although even these strategies currently lack a compelling evidence base, Drs. Simunovic and Baxter wrote.
The study researchers reported no financial conflicts. This study was supported by a grant from the National Cancer Institute.
The editorial writers reported no financial conflicts. Dr. Baxter is supported by a Canadian Institutes of Health new investigator award.
Primary source: Journal of the American Medical AssociationSource reference: Wong SL, et al "Hospital lymph node examination rates and survival after resection for colon cancer"JAMA 2007; 298: 2149-2154. Additional source: Journal of the American Medical AssociationSource reference: Simunovic M, Baxter NN, "Lymph node counts in colon cancer surgery: lessons for users of quality indicators"JAMA 2007; 298: 2194-2195.