Colon Cancer Survival Linked To Number of Lymph Nodes Examined
An analysis of 17 studies from nine countries has found that the more lymph nodes that are removed and examined during surgical treatment of colon cancer, the better the outcome appears to be for patients. The study suggests that removal of the nodes takes away a reservoir for potentially lethal cancer, and that knowing how far a cancer has spread leads to tailored and more beneficial treatment, according to researchers at The University of Texas M. D Anderson Cancer Center.
Investigators say the findings, reported in the March 21 issue of the Journal of the National Cancer Institute, encourage a dialogue amongst physicians regarding the number of lymph nodes removed by surgeons and evaluated by pathologists as a measure of the quality of care that colon cancer patients receive.
"Currently just over one-third of colon cancer patients in the United States are getting an adequate lymph node evaluation," says the study's lead author, George Chang, M.D., assistant professor in the Department of Surgical Oncology at M. D. Anderson.
The results of this study were striking and should help support efforts now ongoing by some medical professional societies and expert panels to consider a minimum number of lymph nodes be extracted and examined during the surgery, continues Chang.
For example, the research team reports that one of the 17 studies examined, a national clinical trial enrolling more than 3,200 patients to look at the effects of chemotherapy on colon cancer recurrence after surgical resection, demonstrated a 14% increase in five-year survival if more than 20 lymph nodes were examined, compared to less than 11 nodes among patients who have Stage II cancers. The survival advantage was even greater - 23% - in patients with Stage IIIA and IIIB cancer if more than 40 nodes were evaluated, compared with less than 11 nodes.
All but one of 17 studies of Stage II cancer showed the same association between the number of nodes evaluated and improved outcome, as did four of six studies of more advanced cancer, Chang says.
"This tells us that surgeons and pathologists involved in the care of colon cancer patients should make every effort to improve their collection and evaluation of lymph nodes."
Removing colon tissue during surgery in a way that captures all of the tumor-associated lymph nodes requires attentiveness, Chang acknowledges. A surgeon needs to trace back the origins of blood vessels closest to the tumor because the lymphatic system, with its nodes, closely tracks with the blood system.
Sometimes the nodes, which filter cancer cells from the lymph, can be difficult for pathologists to find, especially when the lymph nodes are small or when the patient is obese. "Everyone is different," he says. "Some people have more nodes, some people have fewer; nodes can be large and easy to identify or small, and the number may differ depending on which part of the colon contains the tumor. The factors that determine the total number of lymph nodes are not all together known."
These findings also should serve as an empowerment tool for patients in need of colon cancer surgery.
"Health care consumers are told all the time to ask surgeons how many operations they have done, but I think in this case they should ask how often they do colon cancer surgery. Surgeons responsible for the majority of these procedures do them infrequently," says Chang.
Studies have found that 70% of colon cancer resections are performed by general surgeons who do less than 10 of these surgeries a year, and that colon cancers removed by surgeons who perform colon cancer surgery more frequently are more likely to have more lymph nodes examined.
"We are not suggesting surgeons cut out more colon than necessary, but that they abide to the principals for cancer surgery, and that pathologists follow up in kind," Chang says.
Because all of the studies examined were observational, the researchers stress that they cannot definitively say increasing the number of lymph nodes examined leads to improved survival. Such a statement could only be supported by a randomized, controlled clinical trial - which would not be ethically possible to do.
Co-authors of the study include M. D. Anderson's John Skibber, M.D. and Miguel Rodriquez-Bigas, M.D., both professors in the Department of Surgical Oncology and Virginia Moyer, M.D., professor in the Department of Pediatrics at Baylor College of Medicine.