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Trent Study Finds “Chemobrain” Effect Caused by Drugs, not Stress


Chemotherapy’s mild and localized cognitive impairment is
good news for breast cancer patients

November 8, 2006, Peterborough, Ontario

A new study led by Dr. Gordon Winocur, Trent University professor and senior scientist of the Rotman Research Institute, has confirmed that it is the drugs, not psychological stress, that causes the phenomenon of “chemobrain” experienced by breast cancer patients undergoing chemotherapy treatment. 

There has been considerable controversy surrounding the root cause of chemobrain, which is characterized by a decline in memory and other cognitive functions.  Prior to this study, doctors were unable to determine if these negative changes during treatment were the result of the chemo drug side effects or caused by the psychological impact of extreme stress endured by breast cancer patients.

“In our study, we identified learning and memory deficits in the mild to moderate range in the drug-treated mice compared to the controls,” says Dr. Winocur.  These results will help doctors educate their patients more effectively when preparing them for chemotherapy treatment.

The limited degree of cognitive impairment is good news for cancer patients.  “That the deficits were relatively small is encouraging,” noted Dr. Winocur.  “It’s important that cancer patients continue with these drugs and know that if they experience mild to moderate impairments in their cognitive functions, this level of change is potentially manageable.”

Dr. Winocur’s study was conducted in his labs at Trent University over a period of two years in collaboration with Dr. Leslie Kerr, professor of psychology and biology at Trent.  It involved testing the cognition effects of chemotherapy on mice, using behavioural task models in a series of experiments.  These models, which tap into a broad range of learning and memory processes, were developed over several decades by Dr. Winocur at Trent University.  His testing methods were critical to the success of this study as they produce cognition assessments that can be effectively related to humans.  Previous studies into chemobrain failed to generate far-reaching results due to methodological limitations.

The tests involved comparing the performance of mice injected with standard doses of chemotherapy drugs (methotrexate and 5-fluorouracil (5FU)) to a control group of mice who received a saline solution.  Behavioural tasks, such as spatial memory tests and conditional rule learning tests using a water maze, were used enabling researchers to assess various aspects of learning and memory associated with different brain regions.  The specific brain regions targeted by these tests were the hippocampus and the frontal lobes.

The drug treatment group scored lower on the spatial memory task (hippocampus) and the task requiring strategic and working memory components (frontal lobes), especially when there were long delay intervals, compared to the control group.  The drug group was not impaired on a cued memory test or in discrimination learning, tasks that are not affected by selective damage to the frontal lobes or hippocampus.

The localized nature of the mice’s cognitive deficits is another significant finding of this study.  “This indicates that the adverse effects of this treatment regimen of methotrexate and 5FU probably do not extend to all regions of the brain.  It appears that the hippocampus and frontal lobes are primarily affected,” says Dr. Winocur.

The study focused primarily on the short-term effects of the drugs.  Dr. Winocur notes this is important because it raises the possibility that at longer treatment intervals there may have been some recovery of cognitive function.

The study, entitled, “The effects of the anti-cancer drugs, methotrexate and 5-fluorouracil, on cognitive function in mice” was published in the September 2006 issue of Pharmacology, Biochemistry and Behaviour (Vol. 85, Issue 1).  Dr. Winocur also presented his findings at a workshop held during the 8th World Congress of Psycho-Oncology in Venice in October 2006.

Dr. Winocur’s research was supported by a grant from Science and Engineering Research Canada and a Young Investigator Award from the American Society of Clinical Oncology.

One of Canada's top universities, Trent University is renowned for striking a unique balance between outstanding teaching and leading-edge research. The University is consistently recognized nationally for faculty who maintain a high level of innovative research activity and a deep commitment to the individual student. Distinguished by excellence in the humanities, social sciences and natural sciences and increasingly popular professional and graduate programs, Trent is dedicated to providing its students with an exceptional world view, producing graduates who are ready to succeed and make a difference in the world.  Trent's Peterborough campus boasts award-winning architecture in a breathtaking natural setting on the banks of the Otonabee River. Together with its satellite campus in Oshawa, Trent draws excellent students from throughout the country and around the world.  The Rotman Research Institute is part of the Baycrest Research Centre for Aging and the Brain, a world-renowned healthcare and research facility for aging adults, with a strong focus on brain functioning and mental health.


For more information contact:

Brittany Cadence, Communications Officer, (705) 748-1011, ext. 5371