A new study shows that breast cancer metastases form more efficiently while patients sleep. This finding, in a study led by researchers at the Federal Polytechnic School (ETH) in Zurich, Switzerland, could significantly change the way cancer is diagnosed and treated in the future, as published in the journal Nature.
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 all over the world contract the disease. If doctors find breast cancer early, patients usually respond well to treatment. However, things turn much more difficult if the cancer has already metastasized.
To date, cancer research has not paid much attention to the question of when tumors release metastatic cells. Until now, researchers assumed that tumors continuously release these cells. However, the new study by researchers at the ETH Zurich, the University Hospital Basel and the University of Basel has now come to the surprising conclusion that circulating cancer cells that subsequently metastasize arise mainly during the sleep phase of affected individuals.
The tumor is activated
“When the affected person is asleep, the tumor wakes up“, summarizes study leader Nicola Aceto, Professor of Molecular Oncology at ETH Zurich. During their study, involving 30 cancer patients and mouse models, the researchers found that the tumor generates more circulating cells when the body is asleep. Cells that leave the tumor at night also divide more rapidly and thus have a increased potential to form metastasescompared to circulating cells leaving the tumor during the day.
“Our research shows that the escape of circulating cancer cells from the original tumor is controlled by hormones such as melatonin, which determine our day and night rhythms,” says Zoi Diamantopoulou, lead author of the study and postdoctoral researcher at ETH Zurich.
In addition, the study indicates that the time at which tumor or blood samples are taken for diagnosis can influence the conclusions of oncologists. It was an accidental finding along these lines that first put the researchers on the right track: “Some of my colleagues work early in the morning or late in the afternoon; sometimes they also test blood at unusual hours” Aceto explains. The scientists were surprised to find that samples taken at different times of day had vastly different levels of circulating cancer cells.
Hours of sleep
Another clue was the surprisingly high number of cancer cells found per unit of blood in mice in comparison with the humans. The reason was that, like nocturnal animals, mice sleep during the daywhich is when scientists collect most of their samples.
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“In our opinion, these results may indicate the need for health professionals to systematically record the time they perform biopsies,” Aceto says. “It can help make the data truly comparable.”
The researchers’ next step will be find out how these findings can be incorporated into treatments existing oncology drugs to optimize therapies. Within the framework of other studies with patients, Aceto wants to investigate whether different types of cancer behave in a similar way to breast cancer and whether existing therapies may be more successful if patients are treated at different times.