Canadian-led study identifies which colon cancer patients benefit from chemotherapy

New insight is important step forward in personalized cancer care

A new Canadian-led study in the latest issue of the New England Journal of Medicine shows that a simple genetic test can determine if chemotherapy will be effective in treating a patient’s colon cancer, the second leading cause of cancer deaths in North America.
The study, led by doctors and researchers from Toronto’s Princess Margaret Hospital and Mount Sinai Hospital, examined 570 tissue samples from colon cancer patients. Colon cancer, which will kill an estimated 8,300 Canadians this year, is usually treated by a combination of surgery and chemotherapy.

The study determined that patients with a specific mutation in their tumor, called high-frequency microsatellite instability, did not benefit from chemotherapy, which can be a very difficult treatment with significant unpleasant side effects. The study’s findings represent a significant step forward in providing individualized treatment plans for colon cancer patients.

“This study shows that the usual type of chemotherapy is effective for about 83 per cent of colon cancer patients,” said lead author Dr. Steven Gallinger, a surgical oncologist at Mount Sinai Hospital and University Health Network, as well as Professor of Surgery at University of Toronto. “Yet, for nearly 17 per cent of colon cancer patients, the traditional chemotherapy treatment is not helpful, and may even be harmful.”

The study, which also involved doctors and researchers from the United States and France, shows that further investigation is needed to provide alternatives for these patients, such as new drugs that are effective on tumors with high-frequency microsatellite instability.

Testing for this genetic mutation could easily become a regular routine during diagnosis, with the results being used to direct the rational use of chemotherapy in colon cancer.

“Undergoing chemotherapy is not an easy decision. Side effects can include sore throat and mouth, tiredness, increased risk of infection, and in a small number of cases, even serious life-threatening illness,” said Dr. Malcolm Moore, a Princess Margaret Hospital medical oncologist involved in the study. “If we can select the patients most likely to benefit from therapy, we can restrict therapy to that population and spare the remaining patients the trauma of that type of treatment.”