The scientific community believed that breast tumors continuously release metastatic cells, but a Swiss scientific team found that cancer cells that circulate and later form metastases occur mainly during the sleep phase.
This is the main finding of a study of 30 patients and mouse models published in the journal Nature, led by researchers from the École Polytechnique Fédérale (ETH) in Zurich, the University Hospital of Basel and the University of Basel.
Breast cancer is one of the most common forms of cancer, according to the World Health Organization (WHO). Every year, about 2.3 million people get the disease worldwide.
If doctors detect cancer in time, patients usually respond well to treatment. However, things become much more difficult if the cancer has already metastasized, reminds ETH.
Metastases occur when circulating cancer cells separate from the original tumor, travel through the body through blood vessels and form new tumors in other organs.
According to those responsible for the work, previous cancer research has not paid much attention to this issue when tumors release metastatic cells.
This new study led to a “surprising conclusion”: circulating cancer cells that later metastasize mostly during the sleep phase.
Hormones regulated by circadian rhythms control metastases.
“When a sick person sleeps, the tumor wakes up,” sums up study leader Nicola Aceto, a professor of molecular oncology at ETH Zurich.
During the study, which included 30 patients with cancer and mice, the researchers found that the tumor produces circulating malignant cells when the body is asleep.
Cells that leave the tumor overnight also divide faster and therefore have a higher potential for metastasis than cells that leave the tumor during the day.
“Our research shows that the release of circulating cancer cells from the original tumor is controlled by hormones such as melatonin, which determine our day and night rhythms,” added Zoi Diamantopoulou.
Moreover, the study shows that the time at which tumor or blood samples are taken for diagnosis can influence the oncologist’s conclusions.
According to the Swiss center, it was a coincidence that put investigators on the right track for the first time.
The scientists were surprised to find that samples taken at different times of the day had very different levels of cancer cells.
“In our opinion, these results may indicate the need for health professionals to systematically record the time in which biopsies are performed,” says Aceto, emphasizing: “This can help make the data truly comparable.”
The next step for researchers will be to discover how these findings can be incorporated into existing cancer treatments to optimize therapies.
Aceto wants to investigate whether different types of cancer behave similarly to breast cancer and whether existing therapies could be more successful if patients are treated at different times.
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