Study Challenges Colon Cancer Surgery Follow-Up
TUESDAY Nov. 13, 2007 -- A new study is questioning the conventional wisdom of checking on the health of 12 lymph nodes after colon cancer surgery.
These post-op checks have been thought to be a good indicator of patient survival, but new data is casting that notion in doubt.
"What we are finding is that focusing on this quality indicator may not have much positive value for predicting patient outcome," said the study's lead author, Dr. Sandra L. Wong, assistant professor of surgery at the University of Michigan, Ann Arbor.
Wong's team published its report in the Nov. 14 issue of the Journal of the American Medical Association.
The routine examination of 12 lymph nodes after colon cancer surgery has been endorsed by the National Quality Forum, a respected organization backed by such prestigious bodies as the American Cancer Society and the American Society of Clinical Oncology.
However, the Michigan study of more than 30,000 people who underwent colon cancer surgery provided no support for the protocol.
One expert wasn't surprised by the results.
"People have been interpreting information relating the number of nodes examined and survival in a very simplistic way," said Dr. Nancy N. Baxter, assistant professor of surgery at the University of Toronto and co-author of an accompanying editorial. "That relationship is probably pretty complex, due at least in part to the underlying biology of the tumor," she said.
Using information from the Medicare-linked National Surveillance and End Results data base, Wong's team divided hospitals where the surgery was done into four groups, based on the proportion of patients who had 12 or more lymph nodes examined.
They then assessed patient survival rates for each group of hospitals, adjusting for patient and doctor characteristics.
Hospitals with the highest proportion of patients with 12 or more lymph nodes examined tended to treat lower-risk patients and have a higher volume of surgery. After adjusting for these factors, the researchers found no statistically significant relationship between the number of lymph nodes examined and patients' survival after surgery.
The idea of examining lymph nodes to estimate survival does make sense, experts say. That's because death is more likely if the cancer spreads beyond the colon, and the route of spread is typically through the lymph nodes.
However, Wong and her colleagues found that hospitals in the study tended to find the same number of lymph nodes positive for cancer, no matter how many nodes they examined.
There are several possible explanations for this seeming paradox, including individual variations in dissection or surgical techniques, Wong said. More studies looking at further clinical details may get an answer, she said.
Meanwhile, Wong said, the findings indicated a need to reconsider the 12-node rule, because there is a limit to the resources that can be expended per patient, she said. "If we spend a lot of resources to exact the 12-node exam as the standard of care, we're going to miss the opportunity to improve in other ways," she said.
It would be a mistake to focus entirely on this one indicator of quality, she said.
"Further studies are important, but what we need are better quality indicators," Wong said. She said she had no immediate suggestions about the sort of characteristics that should be examined, except that "we need to look at broader indicators."
For her part, Baxter said that perhaps too much emphasis was being placed on node numbers and diagnoses.
"I don't think setting benchmarks for the number of nodes to be examined will change the outcome for a substantial number of patients," she said. "We should concentrate on things we know will help. For example, we know that many patients with stage 3 colon cancer don't get chemotherapy." Stage 3 cancer has spread to the lymph nodes but not beyond them.
"There is a lot of work to be done in terms of getting treatment we know helps patients, to patients," Baxter said.
But the relationship between the number of nodes examined and patient survival should continue to be explored, Baxter said. "There may be some underlying biological factor we could use," she added.
Another expert also said more research needs to be done.
"In many ways, this study confirms a lot of prior findings about lymph nodes and survival," said Dr George Chang, assistant professor of surgical oncology at the University of Texas M. D. Anderson Cancer Center in Houston. "But it highlights the complexity of that relationship."
Even in the quarter of hospitals in which the largest number of lymph nodes were examined, "only 61 percent of patients had 12 looked at," Chang said. "Perhaps examination of a considerably larger number is required to predict survival."
There's more on colon cancer at the U.S. National Library of Medicine.
Posted: November 2007