May 23, 2011

DNA Repair: A Factor for Colon Cancer

(Ivanhoe Newswire) -- A new study shows a person's DNA repair system may play a role in determining if their cancer will recur. Investigators found colorectal cancer patients with defects in mismatched repair -- one of the body's systems for repairing DNA damage -- have lower rates of recurrence and better survival rates.

About 15 percent of colorectal cancers are associated with mismatch repair defects. Researchers say it has never been clear whether these mismatches are linked to cancer recurrence rates, time-to-recurrence and site of recurrence. They also have been unclear about whether such defects affect responses to chemotherapy.

Investigators from the Mayo Clinic in Rochester, Minn., analyzed data from more than 2,000 clinical trial patients who had been treated after surgery with chemotherapy that included 5-fluorouracil (5-FU) -- a standard drug used in colorectal cancer. The patients had either stage II or stage III colon cancer.

Whether or not mismatched repair status influences response to 5-FU has been debatable. Results from this study showed treatment with 5-FU reduced recurrence rates in stage III patients regardless of mismatch repair status but not stage II patients.

The investigators also compared the effects of 5-FU-based therapy in patients thought to have inherited mismatch repair defects versus those whose defects that occurred sporadically. They found 5-FU appeared to reduce recurrences only in those with inherited defects.
"In conclusion, our data demonstrate that patients with defective mismatch repair colon cancers have a statistically significant reduction in their rates of tumor recurrence, a delayed time to recurrence, and better survival rates," the study authors write.

SOURCE: Journal of the National Cancer Institute, May 19, 2011