Chemotherapy regimens, especially those including anthracyclines such as Adriamycin or taxanes such as Taxol, can be neurotoxic. The associated damage can manifest itself in multiple ways, including peripheral neuropathy, cardiac autonomic neuropathy, sleep disturbances, and cognitive dysfunction (chemo brain).
There are no proven drug treatments for chemo brain. Cognitive training interventions have had inconsistent outcomes. On the other hand, regular exercise has been shown to help prevent and improve some aspects of chemo brain. Now a new study has reported that a 12-week exercise program improved cognition among breast cancer survivors, but only when undertaken during the first two years after breast cancer surgery.
Chemo brain
Chemo brain used to be regarded primarily as a psychological phenomenon associated with the stress of breast cancer diagnosis and treatment. However, an increasing number of studies have demonstrated that chemotherapy for breast cancer can be neurotoxic. Studies have reported clear before and after changes in cognitive functioning. Brain imaging and animal studies have also found physical damage in the brain as a result of chemotherapy, including measurable reductions in gray matter.
It is clear that some chemotherapy-associated compounds do in fact cross into the brain, where they have the potential to cause damage to existing nerve cells and disrupt the formation of new ones.
Chemo brain is characterized by reduced verbal fluency, faulty short-term memory and other deficits. This translates into symptoms such as frequent memory lapses, trouble focusing and multitasking, slowed thinking and decision making, and difficulty remembering common words or names. There may be unwelcome glitches in the brain's operations. Unconscious mistakes can occur in tasks that are simple and routine.
Chemo brain can feel like moving through a fog, where the outlines of thoughts are indistinct. Productive thinking itself can become more difficult, so that it takes effort to complete a thought or come to a conclusion. However, symptoms of chemo brain can vary greatly between breast cancer patients.
Studies that have assessed cognitive functioning using comprehensive neuropsychological tests have reported that chemo brain is characterized by impaired verbal ability, reduced information processing speed, and diminished executive functioning. Processing speed refers to the ability to automatically and fluently perform relatively easy or routine cognitive tasks, especially when high mental efficiency (i.e., attention and focused concentration) is required. Executive functioning refers to the ability to organize thoughts and activities, manage time well, prioritize tasks, and make decisions.
Chemo brain does not appear constitute a direct path to dementia in old age. However, while chemo brain normally improves within the first two to three years after treatment, some degree of residual cognitive dysfunction can be persistent.
Latest research reports exercise intervention improves processing speed
The study referenced above was designed to investigate the effects of a 12-week physical activity intervention on measured and self-reported cognitive functioning among breast cancer survivors. The study included 87 sedentary breast cancer survivors with average age 57. Participants were randomly assigned to the exercise program (43 women) or a non-intervention control group (44). Cognitive functioning was measured at baseline and at 12 weeks using the National Institutes of Health Cognitive Toolbox. Self-reported cognition was assessed using the Patient-Reported Outcomes Measurement Information System scales.
Processing speed (as measured by the Oral Symbol Digit subscale) was found to improve significantly among women in the exercise group compared to the control group. The differences in improvement in self-reported cognitive functioning were suggestive of potential group differences, but the results were not statistically significant.
However, greater increased physical activity was found to be associated with greater improvement in both objective and self-reported cognitive functioning in the exercise group, indicating a dose response. Time since surgery turned out to be important: women who were two years or less post surgery were found to have a significant improvement in processing speed, but no such improvement was observed among those who started the exercise intervention more than two years after surgery. The authors conclude that the exercise intervention significantly improved processing speed, but only among those who had been diagnosed with breast cancer within the past 2 years. The results highlight the potential importance of early adoption of an exercise program among patients with breast cancer, according to the authors.
Please see our article on chemo brain for more information.