March 22 (HealthDay News) -- The more lymph nodes that colon cancer patients have removed and examined, the longer they will live after surgery, new research shows.

Unfortunately, not enough patients are having enough these nodes removed and analyzed, the study's authors add.

"Just over one-third of patients are having more than even 12 lymph nodes [the number recommended by one expert panel] evaluated or identified," said study lead author Dr. George Chang, assistant professor of surgical oncology at the University of Texas M.D. Anderson Cancer Center in Houston. "Clearly, we can do more."

But it's not entirely clear how many nodes is optimal, said the researchers, who published their findings in the March 21 issue of the Journal of the National Cancer Institute.

According to the American Cancer Society, colon cancer is the second leading cause of cancer death in the United States (after lung cancer), with about 100,000 new cases diagnosed and more than 40,000 resulting deaths each year.

Some three-quarters of new cases appear to be curable with surgery. Chemotherapy is recommended for patients whose cancer has spread to the lymph nodes (stage III cancer). It is also recommended for some patients without lymph node involvement but with other worrisome characteristics (stage II).

"With colon cancer, the stage at which you are diagnosed at the time of the initial surgery predicts your outcome, so it's critical to properly stage the disease," explained Dr. Jerald D. Wishner, director of colon and rectal cancer surgery at Northern Westchester Hospital in Mount Kisco, New York. "We stage based on the tumor itself and the lymph nodes."

But the accuracy of the pathologist's report could also depend on how many lymph nodes are examined. Having five negative lymph nodes is less reassuring than having 20 negative lymph nodes, for example.

"The first issue is, very simply, are we staging patients properly? How many lymph nodes do we need? What is the cut-off?" Wishner asked. "What do we have to do to appropriately stage patients?"

A U.S. National Cancer Institute-sponsored panel of experts has recommended that at least 12 nodes be examined, but, according to Chang, there is no evidence backing up that recommendation. And, in any event, one study found that only 37 percent of colon cancer patients got adequate lymph node evaluation according to this standard.

In their analysis, Chang and his colleagues reviewed 17 studies from nine countries that looked at colon cancer survival and lymph node evaluation.

All but one of the studies reported that increased survival of patients with stage II disease was associated with an increased number of lymph nodes examined. Four of six studies looking at stage III patients found the same association.

A number of factors can influence the completeness of lymph node evaluation, including the quality of the surgical removal, the quality of the pathologist's analysis as well as characteristics of the tumor and of the patient, Chang said.

"There are a lot of factors," Chang confirmed. "Lymph nodes come from a surgical specimen, so the surgeon is responsible. The pathologist evaluates, so the pathologist is responsible. In obese patients, it is more difficult to identify more nodes. There may be other factors we don't fully understand."

For example, older patients may have fewer lymph nodes. The location of the cancer in the colon may also have an effect.

While all these factors deserve more scrutiny, certain patterns have emerged.

Higher-volume centers and more experienced surgeons tend to identify more nodes and therefore see improved survival in their patients, the experts said, but it's not a hard and fast rule.

"Surgeons who do a lot of colon cancer surgery would be more likely to speak with the pathologist and ensure that all identifiable nodes are indeed identified, and they potentially may have done a slightly different operation than those who may not do colon cancer surgery all the time," Chang said. "But that's not to say that just because you don't do a lot, you don't do it right."

The issue is likely to take on more importance as the science advances.

"As we have more treatment options and modalities, the issues that this paper brings up are going to be that much more critical, because we want to ideally stratify patients so we could individualize therapy," Wishner said.

SOURCES: George Chang, M.D., assistant professor, surgical oncology, the University of Texas M.D. Anderson Cancer Center, Houston; Jerald D. Wishner, M.D., director of colon and rectal cancer surgery, Northern Westchester Hospital, Mount Kisco, N.Y.; March 21, 2007, Journal of the National Cancer Institute