An unexpected discovery: Cancer cells are more active when we sleep?

Some scientists stay up until the early hours of the morning to conduct experiments, while others start working early in the morning. They noticed that the same experimental steps, at different times, would produce different results. Some researchers from the Swiss Federal Institute of Technology (ETH) found that the metastasis of cancer cells was unexpectedly closely related to work and rest and specific hormone levels in breast cancer patient samples and mouse models.

Compared with normal mice, the number of single blood tumor cells in mice with disrupted rhythms was reduced to 1/38~1/282. Even if the rhythm of mice was disrupted, the number of circulating cancer cells still increased when they were resting and decreased when they were active.

Melatonin is a hormone that affects sleep. When the level of melatonin was artificially increased in mice, regardless of whether the mice had normal or disordered rhythms, they would receive a large amount of melatonin 2 hours before resting. After about 3 weeks, it was clearly observed that melatonin caused a significant increase in the number of tumor cells in the blood of mice. This indicates that the process of these cells detaching and escaping from the tumor in situ is controlled by hormones such as melatonin, and melatonin happens to affect the circadian rhythm.

When cancer patients fall asleep, do cancer cells wake up?

To see if this was also true in humans, they recruited 30 female volunteers with breast cancer who were either not receiving treatment or had temporarily stopped treatment.

The research team then collected blood samples from the women at 10 a.m. (awake) and 4 a.m. (deep asleep).

The results showed that most circulating cancer cells (CTCs) and CTC clusters came from samples obtained at night. More circulating cancer cells appeared in samples collected from female breast cancer patients during sleep.

They proved that the cells that would later form cancer metastases did appear and become active during sleep.

References:

https://mp.weixin.qq.com/s/U4P-7cnp5AvAKJEgpPbBCw

Breast cancer spreads at night. Retrieved June 22, 2022 from https://www.eurekalert.org/news-releases/956526?

The metastatic spread of breast cancer accelerates during sleep. Nature (2022). DOI: 10.1038/s41586-022-04875-y