Study: Some Colorectal Cancer Patients May Not Benefit From Chemotherapy

Genetic testing may help one patient in six diagnosed with colorectal cancer avoid unnecessary chemotherapy treatment, according to a report in the New England Journal of Medicine.

A team of international researchers found that chemotherapy, which is common following colorectal cancer surgery, does not appear
to help the 17 percent of patients with a specific genetic feature in their tumour called high-frequency microsatellite instability.

In fact, the researchers said that for these patients, chemotherapy may do more harm than good.

"This is important news because it demonstrates what we've known all along -- that not all colon cancers are the same and not all can be treated in the same way," said Dr. Michael Wosnick, executive director of the National Cancer Institute of Canada.

"Step by step, we're learning more about colon cancer and this discovery means some people could be spared the ordeal of chemotherapy," he said.

All normal cells have so-called "microsatellite" areas where sequences of DNA repeat themselves. If the length of the repeated sequence is longer or shorter than in healthy cells, it can signal a problem. Cells with many sections of abnormal repeats are said to have "high-frequency instability." Cells with a few areas have "low-frequency instability,"

In their study, the researchers analyzed specimens from 570 patients with stage II or stage III colon cancer. Of the total tissue specimens, 16.7 percent exhibited high-frequency instability, 10.5 percent demonstrated low-frequency instability and 72.8 percent were stable.

Chemotherapy after surgery improved overall survival for patients with tumors that were stable or displayed low-frequency instability, but it did not increase five-year survival for patients with high-frequency instability, the researchers said.

Patients with high-frequency instability had a better five-year survival rate when they did not receive chemotherapy than the other patients who did not receive chemotherapy.

"We now know that a simple genetic test could better inform colon cancer patients on whether or not chemotherapy will improve their likelihood of better survival. This is a major step towards personalized cancer care," said Dr. Steven Gallinger of Toronto's Mount Sinai Hospital.

Other sources: New England Journal of Medicine