New research from the Canadian Cancer Trials Group (CCTG) CO.17 trial has identified a new subset of patients with metastatic colorectal cancer who could benefit from taking the drug cetuximab.

Senior investigator Chris O’Callaghan with the Queen’s University-based CCTG worked with lead researcher Geoff Liu from the Princess Margaret Cancer Centre and collaborators from the Australasian Gastro-Intestinal Trials Group (AGITG) on the research.

“With this finding, we believe we can further improve our ability to identify patients with advanced colorectal cancer most likely to benefit from a targeted therapy like Cetuximab.” says Dr. O’Callaghan.

The new research builds on the CO.17 study, an international clinical trial conducted 10 years ago by the CCTG and AGITG. Working with a group of metastatic colorectal cancer patients with few treatment options remaining, researchers determined that cetuximab was most effective for the 60% of patients whose tumours did not have a mutated version of  KRAS, a protein involved in signaling for cell growth.

Cetuximab didn’t work for everyone without KRAS mutations, though, so Dr. O’Callaghan and his colleagues worked to improve the identification of those patients who benefited from the drug. By analyzing archived tissue samples from 572 patients enrolled in the original trial, they were able to define another subset of patients who responded best to the drug.

 “We need to continue to refine our ability to personalize cancer medicine for people with colorectal cancer, keeping in mind that cetuximab is an expensive drug and can have side effects,” Dr. O’Callaghan says. “So instead of only looking at aspects in the tumour, which is where KRAS mutations occur, we examined features of the patients’ normal tissues. This is how we discovered the marker on white blood cells that this subset of patients has in common.”

Researchers are now working to confirm the results in multiple studies, which will be used to guide clinical decision making. Using data from their follow-on CO.20 clinical trial, collaborators from the CCTG and AGITG hope to validate their results.

The research was published in Clinical Cancer Research.