Study Findings May Affect Treatment Of Colorectal Cancer

At the present time, all colorectal cancer patients are treated with a similar approach. It now appears that the disease has two forms that behave quiet differently.

Colorectal cancer is the second leading cause of cancer deaths in North America. An estimated 20,000 Canadians will be diagnosed with the disease this year.

The study establishes that 17 per cent of colorectal patients have a genetic abnormality in their cancer cells called microsatelite instability (MSI), while 83 per cent of patients have a different spectrum of genetic mutations that lead to chromosomal instability (CSI). The research team has determined that colorectal cancer patients with the MSI form of the disease have a better chance of surviving longer and their tumor is less likely to spread throughout the body.

"The study may ultimately lead to changes in the clinical management of colorectal cancer," says Dr. Steven Gallinger, Senior Scientist at the Samuel Lunenfeld Research Institute, general surgeon at Mount Sinai, and Associate Professor of Surgery, University of Toronto.

The MSH research team used data and tumor samples provided by the Ontario Cancer Registry and over 40 pathology departments in the province to study 650 young colorectal cancer patients treated in Central East part of Ontario between 1989 and 1993.

"The most important finding was a significant difference in survival time", explains Dr. Gallinger. "MSI positive cases survived much longer than other colorectal cancer patients."

"At the present time, we treat all colorectal cancer patients as if they have the same disease. This study provides the first evidence that the different genetic pathways that can lead to colon cancer result in tumors which look the same, but behave very differently," says Dr. Alan Bernstein, Director of the Samuel Lunenfeld Research Institute and Professor of Medical Genetics and Microbiology, University of Toronto.

The other members of the research team are: Dr. Mark Redston, associate scientist, SLRI, assistant professor, pathologist, MSH, assistant professor, Department of Laboratory Medicine and Pathology, University of Toronto; Dr. Robert Gryfe, surgical resident, University of Toronto; Dr. Shelley Bull, senior scientist, SLRI, associate professor, Department of Preventive Medicine and Biostatistics, University of Toronto; Dr. Eric Holowaty, director, cancer surveillance unit, division of preventive oncology, Cancer Care Ontario; Melyssa Aronson, genetic councillor MSH, Dr. Eugene Hsieh, pathologist, Sunnybrook and Women's College Health Sciences Centre; and Hyeja Kim, MSc, research technician, SLRI.

The study was funded by a research grant from the National Cancer Institute of Canada.