Breast Cancer Spreads Most Efficiently When Patients Are Sleeping, Study Finds

It is estimated that nearly 170,000 American women are living with metastatic breast cancer, most of whom were initially diagnosed at an earlier stage. Each year, more than 40,000 Americans will die from the disease, as well. Understanding more about how cancer cells spread can open up more avenues for treatment. A new finding out of Switzerland may help do just that.

Researchers from ETH Zurich, the University of Basel, and University Hospital Basel examined when tumors shed metastatic cells. Prior to their study, it was assumed that this process happened continuously. However, according to their findings, published in the journal Nature, cancer cells that later form metastases are largely shed when a person is sleeping.


Zoi Diamantopoulou, lead author and postdoctoral researcher at ETH Zurich, says, “Our research shows that the escape of circulating cancer cells from the original tumor is controlled by hormones such as melatonin, which determine our rhythms of day and night.”

The research involved 30 female cancer patients and mouse models. In both groups, the tumor was found to generate more circulating cells during sleep, with cells that leave the tumor at night dividing more quickly than those shed during the day, which gives them a higher likelihood of forming metastases.

The time of day at which samples were taken also impacted the number of circulating cells, which the team says may impact what oncologists find during tests. This was discovered by accident, as the researchers involved were analyzing samples at a wide variety of times. However, the team says it could mean that doctors may want to be mindful of when samples are drawn.


Nicola Aceto, study leader and professor of molecular oncology at ETH Zurich, says, “In our view, these findings may indicate the need for healthcare professionals to systematically record the time at which they perform biopsies. It may help to make the data truly comparable.”

Going forward, the team hopes to use these findings to improve cancer treatments, possibly changing the time at which they are administered. They also plan to see if other cancers behave the same way.

You can read the study here.

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