Impact of Chemotherapy on the Brain's Circadian Rhythms

Chemotherapy, a common treatment for cancer, has been found to significantly disrupt the body’s natural circadian rhythms in patients. These rhythms are essential for regulating sleep-wake cycles, hormone release, and other vital functions. Notably, nearly half of cancer patients undergoing chemotherapy experience disturbances in their circadian patterns, which can lead to increased side effects and reduced quality of life.

Interestingly, since the primary pacemaker for these biological rhythms resides in the brain, researchers have hypothesized that chemotherapeutic agents may indirectly affect brain function to cause this disruption. However, many chemotherapeutic drugs, like paclitaxel, do not effectively penetrate the brain due to the protective blood-brain barrier.

A recent study led by Leah Pyter at Ohio State University investigated this paradox by exploring whether paclitaxel influences the brain’s circadian clock in mice. Focusing on female mice, which are primarily affected by breast cancer, the researchers assessed gene expression related to circadian rhythms and behavioral responses to light challenges. They observed that, following chemotherapy, the expression of circadian genes in the brain's master clock did not fluctuate as they normally would; instead, their rhythms became irregular. Furthermore, mice treated with paclitaxel showed impaired adaptation to light-based cues that typically help synchronize circadian rhythms.

This suggests that paclitaxel may disrupt not just peripheral tissues, but also the brain’s molecular and behavioral circadian outputs, even if it does not directly target the brain. Zoe Tapp, the study's first author, emphasized that this was a novel observation—that the principal brain clock appears indirectly affected by chemotherapy.

Clinically, these findings highlight the potential importance of managing circadian disruption in cancer patients. Maintaining proper sleep-wake cycles and light exposure might help mitigate some side effects of chemotherapy, potentially improving patients’ quality of life. Future research is needed to determine whether interventions targeting circadian pathways can reduce the adverse effects associated with cancer treatment.

For more detailed information, refer to the study published in eNeuro: DOI: 10.1523/ENEURO.0061-25.2025 (source: https://medicalxpress.com/news/2025-09-chemotherapy-disrupt-circadian-rhythms.html).