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More Is Better, But How Much Is Enough?by Dianne Witter
Two colon cancer patients with similar diagnoses undergo potentially curative colon resections: one remains disease-free five years later; the other survives only six months. George J. Chang, M.D., an assistant professor in M. D. Anderson’s Department of Surgical Oncology, wants to know why. Although some variables remain unknown, evidence increasingly points to the number of lymph nodes resected as an important determinant of outcome. In a recent systematic literature review, Dr. Chang and his colleagues analyzed the results of 17 studies from nine countries and found a surprisingly clear association: in all but one of the studies, the more lymph nodes removed and examined during colon cancer surgery, the better the patient’s survival outcome. The study was published in the March 21 issue of the Journal of the National Cancer Institute. One of the studies included in the review showed that when more than 20 lymph nodes were examined, compared to fewer than 11, there was a 14% increase in the five-year overall survival rate in patients with stage II colon cancers. The survival advantage rose to 23% in patients with stage III cancers when more than 40 nodes were evaluated. The association between lymph node recovery and outcomes is now under study in other cancers as well. “We don’t yet know exactly why increased lymph node harvest affects outcome—there are likely to be many different factors involved,” said Dr. Chang. “But the fact that there is an association between node removal and survival is now crystal clear. Simply being very diligent about the number of lymph nodes we recover is one thing we, as surgeons, could do that could have a big impact on outcomes.” More accurate staging is one apparent reason for the improved outcomes seen with the resection of more lymph nodes, but Dr. Chang feels there are other contributors as well. “Perhaps there is a therapeutic benefit associated with removing more nodes, beyond simply improving stage assignment,” he said. “It also may be that the number of nodes removed is a marker of the quality of care the patient is receiving —that all the members of a patient’s treating team, including the surgeon, pathologist, and medical oncologist, are providing the highest level of care when more nodes are harvested.” Studies have shown that, currently, more than half of the colon cancer resections in the United States do not include adequate lymph node removal and evaluation. But Dr. Chang stressed that this does not mean that surgeons should adopt a new way of performing surgery; rather, they should carefully adhere to the fundamental principles of colon cancer surgery. “This doesn’t mean taking out more of the colon—it means performing a thorough exploration, removing the appropriate amount of the colon from around the tumor site, and removing all of the lymph nodes by dividing the primary feeding blood vessels at their origin,” he said. A number of variables affect how many lymph nodes can be harvested in a given surgery for colorectal cancer, and some of these the surgical team and pathologist cannot control, such as tumor location, patient physiology, and the number and size of lymph nodes in the affected area. “But there are two variables we can control: for the surgeon, the completeness of the surgical resection; and for the pathologist, the thoroughness of the tissue examination, with the goal of recovering all possible nodes,” said Dr. Chang.
Exactly how many lymph nodes should be examined is still a matter of controversy. A panel of experts appointed by the U.S. National Cancer Institute recommended that a minimum of 12 lymph nodes be resected in colon cancer surgery, and several organizations have adopted this guideline, including the American College of Surgeons, the American Society of Clinical Oncology, and the National Quality Forum. Although that number is still somewhat arbitrary, and perhaps on the low side, according to Dr. Chang, it’s a good place to start. “We don’t have all the answers yet, but I think we can begin to make some clinically significant improvements in outcomes with this guideline,” he said. “Resecting and examining a minimum of 12 lymph nodes in colon cancer surgery is a very achievable goal, and it’s probably in the sweet spot where we can see some real population-level improvements in survival.” To illustrate, Dr. Chang did some quick math: approximately 100,000 people in the United States are diagnosed with colon cancer each year, and about 75% of them have disease that is potentially curable with surgical resection. “If we could increase five-year survival by 10% through improved lymph node evaluation—and I think it’s highly likely we could—that would impact 7,000 patients every year.” Dr. Chang hopes the findings about the association between lymph node harvest and outcome will encourage a dialogue among physicians, surgeons, and other medical professionals. The M. D. Anderson study may support further efforts by medical societies to determine the optimum number of lymph nodes to be removed and examined, the relationship between the number of lymph nodes evaluated and the quality of cancer care, and the impact of changing this number. Dr. Chang added that the more accurate prognostic information made possible by optimum lymph node resection will become increasingly important as treatment options increase and therapies become more individually tailored.For more information on this topic or for questions about M. D. Anderson’s treatments, programs, or services, call askMDAnderson at (877) MDA-6789. Other articles in OncoLog, June 2007 issue:
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