TUESDAY, Sept. 13 (HealthDay News) -- Searching for cancer in lots of lymph nodes after colon cancer surgery does not seem to increase patients' chances of survival, a new study finds.
Researchers from the U.S. National Cancer Institute analyzed data on more than 86,000 cancer patients from the Surveillance, Epidemiology and End Results (SEER) cancer registry.
The investigators found that over the past 20 years, there's been a trend toward pathologists evaluating more and more lymph nodes in the hunt for cancer cells that have spread beyond the colon, according to the study in the Sept. 14 issue of the Journal of the American Medical Association.
Though there can be variations in treatment, colon cancer patients whose tumors have metastasized, or spread to the lymph nodes, typically receive chemotherapy, while those with localized tumors are often treated with surgery alone, explained study author Helen Parsons, a public health advisor at the U.S. National Cancer Institute.
Presumably, evaluating more lymph nodes would increase the chances of finding cancer cells that have spread and help to get patients the right level of treatment, Parsons said.
During 1988-1990, about 35 percent of the patients studied had 12 lymph nodes or more evaluated. That rose to 47 percent in 2000-2002 and to nearly 74 percent in 2006-2008, according to the report.
And yet, despite evaluating so many more lymph nodes, pathologists didn't identify many more metastatic cancers.
In 1988-1990, about 40 percent of colon cancers were found to have spread to the lymph nodes, rising only slightly to 42 percent in 2006-2008.
"We found that while the number of lymph nodes patients had evaluated increased dramatically over the past 20 years, it hasn't led to significant increases in the overall proportion of lymph node-positive colon cancers identified," Parsons said.
Still, there was an association between the number of lymph nodes evaluated and survival. Patients who had more lymph nodes evaluated had a greater chance of surviving for five years than those with none or just a few nodes evaluated.
For example, patients with no nodes evaluated were 1.2 times more likely to die than those who had one to eight nodes evaluated regardless of whether the nodes were found to be cancerous or not. Patients who had between 12 and 15 nodes evaluated were 17 percent less likely to die than those who only had between one and eight evaluated; patients who had more than 40 nodes evaluated had a 36 percent decreased risk of death.
Put another way, about 55.4 percent of patients with no nodes evaluated died within five years; that dropped to 46.6 percent of those who had 12 to 15 evaluated and 33.3 percent of those who had more than 40 nodes evaluated.
But since there wasn't a strong link between evaluating more nodes and finding more cancers, researchers concluded that other qualities about the doctors or the hospitals may explain the differences in survival rates, rather than the node evaluation itself.
"Patients who had a large number of lymph nodes evaluated were only slightly more likely to be lymph node-positive than those who had only a few lymph nodes evaluated, and yet the group that got more lymph nodes evaluated had significantly lower mortality," Parsons said. "That suggests that something else . . . is the primary mechanism by which we are seeing the relationship."
Lymph node evaluation is one measure that's being used to assess hospital quality, but the study calls into question whether it's a useful measure, Parsons said. The National Quality Forum and several surgical consensus panels all recommend testing 12 or more lymph nodes, Parsons said.
Prior research has shown that if cancer is going to be found in lymph nodes, the chances are it will be found in the first five or so lymph nodes, and then the odds of turning up cancer drop quickly from there, Parsons said.
"We're not saying we shouldn't evaluate lymph nodes. It's still important. But using this as a measure for reimbursement, or a marker for quality may have a limited impact on improving survival," she added.
In an accompanying editorial, Dr. Sandra Wong, an assistant professor of surgery at University of Michigan, said the research is more evidence that evaluating lots and lots of lymph nodes after surgery for colon cancer doesn't seem to help cancer patients much.
Wong was the author of a 2007 study that found hospitals that did a lot of node evaluation didn't have better colon cancer survival rates than hospitals that did less.
"The theory that evaluating lots of nodes can help you find more positive nodes isn't holding up," Wong said.
But this study found an association with greater survival, which suggests a "missing link" to explain it.
That missing link may lie in the details of the surgery or what treatment the patient received after surgery, information the researchers weren't able to consider, she said. It's a question worth answering, Wong added.
"There is so much focus on finding these lymph nodes," she said. "Those are resources we could be using to improve cancer care, such as providing more colonoscopies or making sure people who have a positive node get chemotherapy."
More information
The U.S. National Cancer Institute has more on staging colon cancer.
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