THE ESSENTIAL
- Researchers have noticed that the human biological clock controls DNA repair.
- This discovery made it possible to identify that radiotherapy is more effective if it is done in the afternoon or evening.
- This phenomenon, called chronoradiotherapy, is observed with prostate and breast cancers, but not lung cancer.
Radiotherapy is one of the treatments most often used to fight cancer. And, it seems that the time at which the rays are performed can significantly influence the effectiveness of the sessions for certain malignant tumors.
This work, carried out by researchers from the Andalusian Center for Molecular Biology and Regenerative Medicine (CABIMER) and the University of Seville, was published in the journal Nature Communications.
Radiotherapy: afternoon sessions would be more effective
In this study, researchers closely studied the DNA of the tumors. This is because cancer cells are generally unable to effectively repair their DNA. This weakness is exploited by radiotherapy, by generating DNA breaks that the tumor cells are unable to repair.
Looking into this phenomenon, the team noticed that the repair of DNA breaks in human cells exhibits a circadian oscillation.“That is, its effectiveness is not uniform, but varies depending on the time of day. During human circadian cycles, repair activity peaks early in the morning, then gradually declines until nightfall, before increasing again during the night.”explain the authors in their communiqué.
They also noticed that this regulation depends on an essential component of the biological clock: the CRY1 protein. “This protein acts as a temporal regulator and its abundance naturally varies during the day/night cycle.”
When CRY1 levels are low – which corresponds to early morning in humans – DNA repair is stimulated. Low levels – usually seen in the afternoon or evening – are associated with slower repairs. This increases the sensitivity of cancer cells to damaging agents such as ionizing radiation. According to these data, it would therefore be more interesting to have radiotherapy sessions in the afternoon or evening.
Chronoradiotherapy: not all cancers respond to it
The conclusions of the Spanish researchers were confirmed by the study of patients’ medical records. It showed that breast cancer patients with tumors expressing high levels of CRY1 were found to be more sensitive to radiotherapy.
“Moreover, a retrospective analysis of patient data from Virgen Macarena University Hospital demonstrated a significant difference in overall survival depending on the timing of irradiation: treatment administered in the afternoon or evening, when CRY1 levels are naturally higher, made tumor samples more sensitive to radiotherapy and improved patient prognosis.”
This effect has also been observed in patients affected by prostate cancer. On the other hand, it was not present in those with lung cancer or gliomas.
The team believes that this work “pave the way for exploring the therapeutic potential of irradiation at specific times of the day, a phenomenon known as chronoradiotherapy”.
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date:2026-02-15 09:45:00