Analysis of 17 studies from nine countries shows that outcome after surgery for colon cancer improves as the number of lymph nodes removed for examination increases, either because a reservoir of potential cancer cells is removed or because determination of existing spread of disease enables better postoperative treatment planning, according to an article in the March 21 issue of the Journal of the National Cancer Institute.

The researchers, from the University of Texas M. D. Anderson Cancer Center, encourage a dialogue among 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," said the study's lead author, George Chang, MD, assistant professor in the Department of Surgical Oncology at M. D. Anderson.

In one of the studies, a national clinical trial of more than 3,200 patients with Stage II disease designed to examine effects of chemotherapy on colon cancer recurrence after surgical resection, demonstrated a 14 percent increase in five-year survival if more than 20 lymph nodes were examined compared with survival if fewer than 11 nodes were removed. The survival advantage was even greater - 23 percent - in patients with Stage IIIA and IIIB cancer if more than 40 nodes were evaluated compared with survival if fewer than 11 nodes were removed.

All but 1 of 17 studies of Stage II cancer showed the same association between the number of nodes evaluated and improved outcome, as did 4 of 6 studies of more advanced cancer.

Chang said, "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."

Sometimes lymph nodes can be difficult for surgeons to find, especially when they are small or the patient is obese. "Everyone is different," Chang said. "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."

Studies have found that 70 percent of colon cancer resections are performed by general surgeons who do fewer than 10 procedures a year, and 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 said.

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.