DNA mismatch in some early stage cases makes therapy of little benefit, shortens survival
FRIDAY, May 16 (HealthDay News) -- Colon cancer patients with a specific subset of the disease don't need to receive chemotherapy. In fact, not only does chemotherapy not benefit this group of patients, it may actually harm them, a new study found.
"If you are found to have [this type of colon cancer], then you should not be treated with chemotherapy. Surgery alone would be standard treatment," said Daniel Sargent, lead author of the study and a professor of biostatistics at the Mayo Clinic in Rochester, Minn.
"In our data, patients who have [this type of cancer] who had surgery alone had a 93 percent survival at five years. In our study, chemotherapy actually lowered survival to 75 percent. So, we have a group of patients who can be spared the toxicity, the expense and the inconvenience of treatment and have a very good outcome even without any [chemotherapy] treatment," Sargent said.
The findings, presented Thursday at the American Society of Clinical Oncology annual meeting, in Chicago, confirm previous research and now give physicians a clearer roadmap for treatment, the study authors said.
About 15 percent of colon cancer tumors are known as deficient DNA mismatch repair (dMMR) tumors, because they have lost the ability to repair DNA damage. This particular type of tumor seems to be less aggressive than other forms of colon cancer, the researchers said.
A study published by the same group of researchers in 2003 in the New England Journal of Medicine also found that this subset of patients did not benefit from standard chemotherapy for colon cancer. Because the finding was so novel, the results needed confirmation before they could be incorporated into clinical practice. This new study offers that confirmation, the researchers said.
"We're talking about patients with early stage colon cancer. These are patients who sometimes get chemo and sometimes do not," Sargent said. "We have sought for a long time to try to determine if there was a way to predict which patients might benefit from chemo and which might not."
But, Sargent added, "we felt that in order to really recommend this in clinical practice, we needed to validate it."
The new study analyzed data from 1,027 patients in the United States as well as Canada, France and Italy who had participated in previous trials. Sixteen percent had dMMR.
"The goal was to validate that the 15 percent of patients who have defective mismatch repair did not receive any benefit from 5-FU therapy, and that is indeed exactly what we found," Sargent said.
"We now feel this is appropriately validated for clinical use," he added.
In fact, there is already a simple test for this type of cancer.
"The test is available and, in a patient with stage 2 disease being considered for treatment with chemotherapy, we think that this test would be useful," Sargent said.
The National Cancer Institute has more on colon cancer.
SOURCES: Daniel Sargent, Ph.D., professor of biostatistics, Mayo Clinic, Rochester, Minn.; May 15, 2008, presentation, American Society of Clinical Oncology annual meeting, Chicago
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